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Canyon Lake Hydrilla:





Canyon Lake Sunset

Notably one of the prettiest rivers in Texas, the Guadalupe flows soft and slow with its crisp blue-green waters and legendary cypress trees that dot the shoreline. The river boasts one of the state's most popular destination for floating, boating, camping, fishing, and hiking. Along its banks, the terrain changes like flip movies in our minds. The headwaters flow off Hill Country peaks in Kerr county, and then it courses its way through a total of 230 miles. It cuts through limestone cliffs to a depth of 909 feet above sea level only to rise again on the other side of Canyon Dam and form a 3-foot deep channel traversing campgrounds and tube chutes. The slow flow of the river makes it the most popular tubing river in Texas.

Venturing eastward, the Guadalupe continues to wide its way through East Texas's black dirt prairie lands fueling hydroelectric energy to 6 stations and multiple municipalities, including SAWS (San Antonio Water System). Its coastal plain becomes a birding habitat, providing cover for endangered whooping cranes and the Texas blind salamander. Eventually, the river meets its course, dumping into the Texas Gulf Coast.

The Guadalupe River Basin (GRB) is alive in the summertime because of its popularity with campers, RV'ers, tubers, and paddlers. The cities along the Guadalupe boast millions of dollars in annual revenues from eco-tourism related to the river.  Kerrville, Comfort, Boerne, New Braunfels, Seguin, Cuero, Victoria, Gonzales all benefit in income and tax revenue from river-related activities.  Fishing along the Guadalupe is renowned for bass, trout and striper, even channel cats. In New Braunfels alone, 5% of the city's revenues come from river parking and river-related income, exclusive of the additional 10% of tax revenues from lodging and eating establishments during the summer tubing season.   The river provides jobs to hundreds of workers in the summertime, one end to the other.


So, what would happen if the river stopped flowing?

"Impossible," you say?   A river that has been running for thousands of years to stop flowing?  Whatever could cause such a drastic reversal.  In the past, this river has sustained in drought and flood, but it has never ceased to regenerate itself. Imagine this.  Within one to two decades, this river could stop flowing.  The cause will not be an external environmental impact to the Guadalupe, rather an internal environmental impact.  This impact is called Hydrilla.
FACT: Hydrilla is named after Hydra, the 9‐headed serpent of Greek mythology, because it can grow an entirely new plant from a tiny stem fragment.

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Hydrilla is a submersed macrophyte native to the warmer areas of Asia. It was first discovered in the United States in 1960. 'Hydrilla has a highly specialized growth habit, physiological characteristics, and reproduction makes this plant well adapted to life in submersed freshwater environments. Consequently, Hydrilla has spread rapidly through portions of the United States and become a serious weed." 

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Picture this: Johnny wins a fish at the state fair, buys a fishbowl, and puts in some aquarium grass (aka, Hydrilla) for the fish to use as cover.  Then Johnny's fish dies.  His parents take the fish to the river to let it swim forever, and they ceremoniously dump the water, including the Hydrilla, into the river.  


The grass establishes, growing 4" a day and spreading. A fisherman comes along and flyfishes for white bass along that bank. He hangs up on the grass and pulls off a piece of it.  He then packs up and heads downriver to do some more fishing, casts into the river, and, voila, Hydrilla is now in another new section.


Uncle Sid takes the boat out skiing with the kids.  He gets shallow during a run and backs into some hydrilla.  When he floats the boat back off the shallows, he takes with him pieces of Hydrilla and chops them into many little slices. These slices float downriver through the dam pipe and land in the river below the dam.  


Now three different people unwittingly move an invasive waterway plant downstream. "Human agency plays a key role in the processes of biological invasions. This comprises not only the human role in the configuration of driving forces or in the perception of the impacts but also the conceptualization of alien species themselves as an environmental problem."

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Just How Invasive is Hydrilla?

Initially, Hydrilla was brought into the U.S. to sell as an aquarium plant.  Within 50 years, it is now in 30 states waterways, wreaking havoc with rivers across the south. It is already present in 30 parishes in Louisiana and much of Florida and is slowly invading Texas. 

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Hydrilla can grow 1 to 4 inches a day.         
These adaptations allow it to out-compete other plants for space to grow. In fact, Hydrilla is so successful it can double its biomass every two weeks during the summer and can fill the entire water column up to 20 feet deep, therefore creating a monoculture- a term used to describe areas dominated by a single species, as opposed to a regular ecosystem that contains multiple species.
Water flows slowly due to the density of these stands of Hydrilla.

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Hydrilla thrives in freshwater environments under 3 feet in depth (but can grow in as much as 30' deep).  Except for a few reservoir lakes, almost the entire Guadalupe river fits this criterion. It will take over shallow coves and riverbeds rather quickly. 

Hydrilla in Canyon Lake

Imagine an establishment of Hydrilla around the 3rd crossing of River Road.  The entire river bed, blanketed with Hydrilla, would shut down all river-related activities within two years. How far away are we from that?  Not far at all.  In 2019, evidence of Hydrilla was spotted upstream in Canyon Lake on the far western edge of the river.  Today, stands of Hydrilla are beginning to overtake some coves popular with fishermen on the west end of Canyon Lake.   It will not take much time for fragments to begin establishing below the dam, choking off any fishing or tubing, and restricting water flow downstream.

At the same time, water lily's have choked the river in the Ingram area with an established colony today.  Water lilies invade the river in similar fashions to Hydrilla. However, Hydrilla has several adaptations that allow it to be more so successful:

  1. It can tolerate lower light conditions than most aquatic plant species, which allows it to begin photosynthesizing earlier in the morning, giving it an advantage. 

  2. It spreads efficiently through both tubers and turions.

  3. There are no native predators that eat Hydrilla, and so their growth is not checked.

Characteristics & Damage Caused

These adaptations allow Hydrilla to out-compete other plants for space to grow. Monocultures can be harmful when they limit the ability of animals in the area to find food or habitat and by preventing the growth of native plants, effectively reducing biodiversity.            That benefit once thought to be helpful to fish ends up harming the fish and wildlife. Hydrilla causes substantial economic hardships, interferes with various water uses, displaces native aquatic plant communities, and adversely impacts freshwater habitats. In a recent study in the southeastern United States, Florida spends millions of dollars annually on mitigation of Hydrilla.  An article on the economic impact stated:

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"Although Hydrilla can provide habitat for fish, it unbalances the predator-prey relationships of some fish. Some predator fish (like sunfish and bass) attack their prey by ambushing them and benefit from the additional cover provided by Hydrilla. However in the long-term, this can lead to an overall decline in the fish population, and eventually even the fish that prefer cover cannot hunt when Hydrilla becomes too dense."

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There are other implications to establishing Hydrilla.  Wherever it has taken a stand, the results are: 


  • diminished or decreased oxygen levels

  • higher levels of bacteria

  • an algae bloom in the water


Hydrilla also harms fish because it depletes oxygen levels in the water. Hydrilla, like all plants, gives off CO2 and uses oxygen during the nighttime (although the opposite is true during the day), which can bring oxygen levels to dangerously low levels for fish. Additionally, an increase of Hydrilla can cause an increase in released nutrients from sediments that cause algae blooms, again depleting oxygen levels.

Hydrilla also retains heavy metals.  Recently, the Texas Commission on Environmental Quality published a river health report.  They sampled at different points of the Guadalupe from the headwaters to the coast.  Low or depressed dissolved oxygen levels were observed at multiple points, and excessive algae, bacteria, and biotoxins were all reported. The issue has caused New Braunfels to add a budgetary item in 2021 to remove dissolved oxygen at $1,685.00 annually.  But I think we will need a bigger boat.

The USGS has required that new stands of Hydrilla be reported, especially in waterways that connect to seas.   Given the Guadalupe is a watershed that connects to the gulf, one could infer that sea grants similar to what was done in North Carolina might be an option for the GRB to investigate.  Reporting is requested on all invasive species to local officials and the USGS online at or by calling 877-7867-267 (877-STOP-ANS) for all non-native species.   Reporting is critical when the region in question is also a habitat for endangered species.

And then there is this gem: another relationship to note is the favorable environment hydrilla provides for the increased establishment of invasive zebra mussels (in which Canyon Lake has been deemed 'infested'. Michelan writes:

"The invasive aquatic macrophyte Hydrilla verticillata facilitates the establishment of the invasive mussel Limnoperna fortunei in Neotropical reservoirs. Furthermore, this plant has different attached algae, which may be more beneficial for mussels. Thus, as a response to the facilitation suggested by our work, the mussel has greater opportunities to succeed in habitats colonized by the non-native H. verticillata. Although we have not evaluated the effects of this facilitation on aquatic communities or the ecosystem, our results could represent the first step of an invasional meltdown.

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Hydrilla poses severe threats to the economies of communities surrounding infested bodies of water. Hydrilla can reduce water flow in canals and ditches up to 85% and clog or damage dams, power plants, and other water control structures. Hydrilla's negative effect on fish populations can also adversely affect anglers and fishermen, and heavy infestations interfere with boating and swimming, as the plant increases the risk of drowning.

Hydrilla's dense foliage poses significant safety risks for recreational boating and swimming. It can cause individuals to get wrapped up in the plant and be unable to free themselves, resulting in drowning in even the best swimmer. In May of 2018, a drowning occurred at Lake Pflugerville. Texas Parks and Wildlife crews had trouble recovering the man due to dense Hydrilla.  Two years earlier, Craig Klugen, a triathlete who had spent nearly 40 years training as a swimmer, had almost drowned trying to free himself from Hydrilla during a training event in Lake Pflugerville.  He warned others about the dangers of swimming with Hydrilla.  Luckily, the support crews were standing by and freed Klugen.  But less than two years later, a man died in Lake Pflugerville while attempting to get free of Hydrilla.        In 2020, a Fort Hood soldier died tangles in Hydrilla while swimming in Stillhouse Canyon Lake. Crews from the Army Corp. of Engineers commented on how Hydrilla hampered recovery efforts in this drowning.

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Bird populations are affected by declines in fish populations and can also be harmed by toxic blue-green algae that grow on hydrilla leaves. In the 1990s, bald eagles were killed off in the Savannah river due to eating tainted prey that had consumed these algae. Every year in Texas, this algae shows up where Hydrilla has established.  It has sickened wildlife and pets alike. 

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Hydrilla management techniques have been developed, but sufficient funding is not available to stop the spread of the plant or implement optimum management programs. Educational efforts to increase public and political awareness of problems associated with this weed and the need for adequate funding to manage it are necessary.
A recent study by Cornell indicates:

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A model was created to predict the costs and benefits of invasive species control within just 13 of the 454 public lakes and rivers in Florida. The findings show that consistent invasive species control is necessary and funding, for this is extremely important. The value of fishing activity alone on the 13 lakes was estimated to hold a value in excess of $64.78 million per year, and the steady-state net benefit of the status quo control strategy is $59.95 million. The model also predicted that a single one-year lapse in control would lead to a 20.67% decrease in recreation and twice the amount of costs in long-term management. These results show that control policies are extremely important and necessary when dealing with Hydrilla and other invasive aquatic species and even one lapse in control can be detrimental.

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Removal Options

Comal County has $7,330 budgeted for 2021 for non-native species removal.   To coin an old Sesame Street phrase, which one of these is not like the other?   We are going to end up having to deal with it at some level.  Either the impact will be felt in reduced revenues and passed along tax burden, reduced property values, decreased employment opportunities, or we will have to cover the costs to mitigate it and retain these through offsetting the negative impacts.   These factors can lower the value of lakeshore properties and tax revenue in affected areas, leading to a decline in the economy.

Based on experiences with Hydrilla in Florida and South Carolina, New York state is expecting to pay $10,000,000+ per year in perpetuity plus millions in lost tax revenue from reduced property and sales taxes on their lake hydrilla issues.
Should there be an effort to mitigate and address the establishment of Hydrilla ahead of the point of no return?   Perhaps there should. If so, then there are multiple ways to attack the issue to get the river healthy again.   Here are just a few, along with their pros and cons.    

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Hydrilla Canyon Lake Treatments

Two area lakes infected with Hydrilla chose different methods of eliminating the issue.  Lake Conroe was infested in the 1970s, 1997, 2003, and again in 2008, until TPWD and SJRA introduced Triploid grass carp and used herbicide to eliminate the problem effectively. Their issues were indeed severe, at times growing 4 acres a day.  It created mats of Hydrilla, which attracted snakes and mosquitoes. By 2019, native plants had reestablished, supporting the fish populations, and grass carp were reintroduced to supplement the population lost to mortality.   However, in 2020, a small 1/10th acre stand of Hydrilla was once again spotted and immediately addressed with herbicide.   Lake Conroe has been controlled in a cooperative effort between Texas Parks and Wildlife, the San Jacinto River Authority, and several angling and Lake associations.

Hydrilla was also discovered on Lake Austin in 1999. Lake Austin also saw the influx of zebra mussels that have a symbiotic relationship to Hydrilla. Hydrilla and zebra mussels got wrapped into water intakes, causing extensive repairs in the water system and hampered waterway movement. By 2002, it had grown to 320 acres but had dropped in 2005 to only 6 acres by introducing 8000 grass carp.  Lake Austin has been successful in keeping Hydrilla at bay.


Hydrilla has now established in the western end of Canyon Lake, a lake very popular for boating, fishing, and swimming that feeds downstream river recreation and hydroelectric and water systems in the lower Guadalupe River Basin. In 2014, zebra mussels were first spotted in Canyon Lake.  Then in the summer of 2020, Canyon Lake resident,  Mr. Bryant  Bonner, noticed Hydrilla mats showing up between the peninsula in Cordova Bend and Cranes Mill Park. The Army Corp. of Engineers partially owns both landmasses.  He notified Texas Parks and Wildlife (TPWD), who governs the fisheries and aquatic life for the Guadalupe River and Canyon Lake, and they became active in the investigation.  The TPWD completed an assessment for all three governing bodies (The Army Corp. of Engineers, GBRA, and TPWD).  Mr. Bonner commented how grateful he was for TPWD's leadership in this manner. Still, when the initial assessment was completed, it showed just under 40 acres of the 8,308-acre lake infested, so all three bodies decided not to take any action to see if the winter would have an impact.  As readers will recall, we had one of the coldest winters (2020-2021) that included the great winter storm in February 2021, but it had no impact on the evasive Hydrilla (it more than likely strengthened it). 

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Mr. Bonner did not stop investigating options on the offhand chance that the Hydrilla returned in the spring of 2021 – he knew it would, given what he had personally seen and experienced at Lake Austin.  He researched ways to remove the Hydrilla and found a product named ProcellaCOR that had been touted as effective in safely eliminating the Hydrilla and had been recently used by TPWD and Army Corp. of Engineers on other Texas lakes to success. He worked with the amazing TPWD staff to submit the proper application for removing the Hydrilla, and TPWD and GBRA initially approved it.

However, when the application made its way to the Army Corp of Engineers Ft. Worth District (which is the body that controls most of the geographical area in Texas – including Canyon Lake), the application was denied.  TPWD informed Mr. Bonner of the application denial and asked (again) that the Army Corp. of Engineers assess the situation. By this time, the 40 acres of Hydrilla had expanded to well over 400 acres in the summer of 2021 (now 6% of the entire water body growing 10x in a single year), and it is anticipated to continue to expand at a similar pace unless the governing bodies take action. The 40-acre treatment is still showing as "approved" on the TPWD website for August of this past year.  It has now become a 400-acre problem. Within the same month that the 40-acre mitigation would have occurred, the Army Corps of Engineers treated 66 acres at Raystown lake, representing less than 1% of that lake's surface.


When lake levels are closer to full, the Hydrilla is far less noticeable at the immediate surface of the lake. It lies lurking just below the surface, posing a serious danger to all citizens.  The boating channel around Cranes Mill has been reduced from over 500+ feet across to a mere 35-40 feet. There have already been reports of near-drownings in the swimming areas infested with Hydrilla late summer of 2021.  In addition, the Hydrilla is spreading multiple miles up and down river from its initial infestation point and is creating mats in all small coves and nooks.  With the recent flooding, debris settled into the mats of Hydrilla broke off pieces, and these Hydrilla fragments are indeed headed downstream towards the dam area.  If Hydrilla establishes below the dam, the financial impacts of downstream cities and tourism will be exponential.

Conclusion: We are Facing A Giant.

We no longer have a choice.  We will either deal with the situation head-on and find intelligent, informed ways to address the issues at hand.  Or the decision will be made for us.   If we choose the latter, it will cost us dearly.  It will take away our river, tourism, and endangered species and replace them with swampy, algae bloom-infested waterways rife for mosquito production and disease.   If we turn our heads in apathy, begging for the next generation to address it, it will be too late.  We need to step up as an entire interconnected community from the coast to the headwaters for the good of all the people, creatures, and industries along this waterway. Apathy is not an option. What we don't get is not to choose. The time to act is now. We strongly encourage you to reach out to your elected officials and let your voice be heard! We will not let our beautiful Canyon Lake go to waste, damage our locally home values and economy and risk the lives of our friends, family and visitors to our lake.


Ref 1: Langeland, Kenneth A. "Hydrilla Verticillata (L.F.) Royle (Hydrocharitaceae), 'The Perfect Aquatic Weed.'" Castanea 61.3 (1996): 293–304.

Ref 2: W. T. Sousa, and Z, “Hydrilla Verticillata (Hydrocharitaceae), a Recent Invader Threatening Brazil’s Freshwater Environments: A Review of the Extent of the Problem.” Hydrobiologia 669, v.1, (2011): 1–20.

Ref 3: Rosa Binimelis, Iliana Monterroso, and Beatriz Rodríguez-Labajos, “A Social Analysis of the Bioinvasions of Dreissena Polymorpha in Spain and Hydrilla Verticillata in Guatemala,” Environ Manage 40. v 4 (2007): 555–66.

Ref 4: “Hydrilla.” LSU AgCenter, May 21, 2018. species/Hydrilla.

Ref 6: “Economic Impacts of Hydrilla.” Cornell Cooperative Extension, n.d.

Ref 7: “Economic Impacts of Hydrilla.” Cornell Cooperative Extension, n.d.

Ref 8: “Economic Impacts of Hydrilla.” Cornell Cooperative Extension, n.d.

Ref 9: Thaisa S. Michelan, Márcio J. Silveira, Danielle K. Petsch, Gisele D. Pinha, and Sidinei M. Thomaz. “The Invasive Aquatic Macrophyte Hydrilla Verticillata Facilitates the Establishment of the Invasive Mussel Limnoperna Fortunei in Neotropical Reservoirs.” Journal of Limnology 73.3 (2014).

Ref 10: “Economic Impacts of Hydrilla.” Cornell Cooperative Extension, Economic Impacts

Ref 11: “Economic Impacts of Hydrilla.” Cornell Cooperative Extension, Economic Impacts

Ref 12: Kenneth A. Langeland, “Hydrilla Verticillata (L.F.) Royle (Hydrocharitaceae), ‘The Perfect Aquatic Weed.’” Castanea 61.3 (1996): 293–304.

Ref 13: Stephen D. Shivers, Stephen W. Golladay, Matthew N. Waters, Susan B. Wilde, and Alan P. Covich. “Rivers to Reservoirs: Hydrological Drivers Control Reservoir Function by Affecting the Abundance of Submerged and Floating Macrophytes.” Hydrobiologia 815.1 (2018): 21–35.

Ref 14: “Economic Impacts of Hydrilla.” Cornell Cooperative Extension, Economic Impacts

Ref 15: “Hydrilla.Pdf,” n.d.,What if Hydrilla is allowed to spread uncontrolled to Cayuga Lake, the Finger Lakes & Great Lake

Ref 16: Hydrilla rediscovered on Lake Conroe, Katy News, 10/14/2020.


Al-Zurfi, S. K. L., and H. H. M. Al-Tabatabai. "Aquatic Plant (Hydrilla Verticillata) Roles in Bioaccumulation of Heavy Metals." The Iraqi Journal of Agricultural Science 51.2 (2020): 574–84.

Binimelis, Rosa, Iliana Monterroso, and Beatriz Rodríguez-Labajos. “A Social Analysis of the Bioinvasions of Dreissena Polymorpha in Spain and Hydrilla Verticillata in Guatemala.” Environ Manage 40.4 (2007): 555–66.

Doyle, Robert D., and R. Michael Smart. "Effects of Drawdowns and Dessication on Tubers of Hydrilla, an Exotic Aquatic Weed." Wees 49.1 (2001): 135–40.

Gordon-bradley, N., N. Li, and H. N. Williams. "Bacterial Community Structure in Freshwater Springs Infested with the Invasive Plant Species Hydrilla Verticillata." Hydrobiologia 742.1 (2015): 221–32.

Hussner, A., I. Stiers, M. J. J. M. Verhofstad, E. S. Bakker, B. M. C. Grutters, J. Haury, J. L. C. H. van Valkenburg, G. Brundu, J. Newman, et al. "Management and Control Methods of Invasive Alien Freshwater Aquatic Plants: A Review." Aquatic Botany 136 (2017): 112–37.

"Management and Control Methods of Invasive Alien Freshwater Aquatic Plants: A Review." Aquatic Botany 136 (2017): 112–37.

Kirk, James P., Kenneth L. Manuel, and Scott D. Lamprecht. "Long-Term Population Response of Triploid Grass Carp Stocked in Piedmont and Coastal Plain Reservoirs to Control Hydrilla." North American Journal of Fisheries Management 34.4 (2014): 795–801.

Langeland, Kenneth A. "Hydrilla Verticillata (L.F.) Royle (Hydrocharitaceae), 'The Perfect Aquatic Weed.'" Castanea 61.3 (1996): 293–304.

Michelan, Thaisa S., Márcio J. Silveira, Danielle K. Petsch, Gisele D. Pinha, and Sidinei M. Thomaz. "The Invasive Aquatic Macrophyte Hydrilla Verticillata Facilitates the Establishment of the Invasive Mussel Limnoperna Fortunei in Neotropical Reservoirs." Journal of Limnology 73.3 (2014).

Rivers, Blanco. "Appendix A – Hydrology and Hydraulic Engineering" (n.d.): 50.

Shivers, Stephen D., Stephen W. Golladay, Matthew N. Waters, Susan B. Wilde, and Alan P. Covich. "Rivers to Reservoirs: Hydrological Drivers Control Reservoir Function by Affecting the Abundance of Submerged and Floating Macrophytes." Hydrobiologia 815.1 (2018): 21–35.

Sousa, W. T., and Z. "Hydrilla Verticillata (Hydrocharitaceae), a Recent Invader Threatening Brazil's Freshwater Environments: A Review of the Extent of the Problem." Hydrobiologia 669.1 (2011): 1–20.

"Center for Aquatic and Invasive Plants | University of Florida, IFAS," n.d.

"Economic Impacts of Hydrilla." Cornell Cooperative Extension, n.d.

"Guadalupe River Basin: Assessment." Texas Commission on Environmental Quality, n.d.

"How to Control Hydrilla - AquaPlant: Management of Pond Plants & Algae." AquaPlant, n.d.

"Hydrilla." LSU AgCenter, May 21 2018. species/Hydrilla.

"Hydrilla.Pdf," n.d.

"Lake Environment: Hydrilla Linked to Deadly Disease | Kerr Lake Guide | Everything About The Lake," n.d.

"New Braunfels 2021 River Season Revenue Returns to near Pre-Pandemic Levels · NewsKudo." NewsKudo, October 15 2021.

"New Braunfels, TX - Official Website | Official Website," n.d.

What is Hydrilla
How Invasive is Hydrilla
Damage Hydrilla Will Cause
Take Action
Removal Options
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