Balancing conflicting public interests, Watershed Protection aims to promote native aquatic vegetation

Austin’s reservoirs do a lot of double duty. They’re known both as top-tier recreation spots for Central Texans and our source of dwindling drinking water. Subject to invasive species, drought and big rainfall events that bring in pollutants, they’re still doing remarkably well, all things considered, a reservoir ecologist told the Environmental Commission on Wednesday. 

Aquatic vegetation – the big mats of plants and algae that have become more prevalent over the past couple of years on Lady Bird Lake and, to a lesser extent, Lake Travis – was the focal point of the presentation by Brent Bellinger, lead reservoir ecologist with the Watershed Protection Department. Though the vegetation is annoying to the recreational kayaker, his pitch was that “as we get more native vegetation, that’s good – that tends to support more bugs and more diversity.” Most importantly, “plants help with water quality.”

Unfortunately, drought conditions promote the growth of cyanobacteria on that vegetation, which is the toxic algae that’s been killing dogs since 2019. The city is in year five of monitoring the algae situation in reservoirs, “and everybody’s looking for that all-clear that they can just let their dogs run free. Unfortunately, I cannot give that to the public at this time. It just waxes and wanes.” One of the causes of toxic algae – invasive zebra mussels brought in on boats by irresponsible lakegoers back from vacation – has been undergoing a “pretty dramatic boom and bust cycle,” which is behavior typical of nonnative species, Bellinger said. The city is in its fourth year of a pilot with the company EutroPHIX that now produces an algae-mitigating product called lanthanum modified bentonite, to “mixed” results.

Though Watershed Protection’s main function is environmental stewardship and the protection of Austin’s precious drinking water, the department still must balance other interested parties, like concessionaires including sunset cruises, rowing and bat-viewing on Congress Avenue, as well as homeowners whose properties come up to the water. Another common use is governed by a different entity: Texas Parks and Wildlife Department manages the state’s reservoirs for fishing. 

“We’re trying to work that balance between all user groups,” Bellinger said. “When you have aquatic vegetation growing out there, you can get some conflicting perspectives – recreational users don’t want much vegetation. Bass fishermen want to fish the edges, so they love dense vegetation.”

Back in 2002, after a large flood event, an invasive plant called hydrilla was moved downriver and caused “a few hundred thousand dollars worth of damage at the time,” Bellinger said. “We can’t have these primary functions of the reservoirs being negatively impacted by these plants.” So the city stocked the reservoir with nonreproducing grass carp, meant to eat up the hydrilla. They did so successfully, but then an unforeseen side effect conflicted with fishermen’s interests: the lack of vegetation made bass much skinnier. 

The city’s goal is to maintain a 15 percent to 25 percent balance of vegetation, ideally native, because they aren’t as dense and are generally better for the ecosystem. That has largely been successful: “In 2023,” Bellinger said, “we started to see vegetation on the rebound.” But “homeowners are starting to notice it’s starting to block boat docks, people are wondering what they can do for management, when are we going to put the carp back,” he said. “Everything that’s old is new again, and at some point, the hydrilla will probably come back and it’ll be something we need to address.” But for now, they want to hold off “as long as possible” on cutting back vegetation to give native species a chance to get reestablished and outcompete the nonnative species.  

There is a way homeowners can clear the plants with permits from the state and city, but anytime a homeowner wants to build a dock or put in a beach on Lake Austin, there’s a strict requirement to replant with native vegetation. There’s never been a systematic review done of these efforts. At the next Environmental Commission meeting, Bellinger says he’ll present the first study of what happens when that management is left to homeowners: “Spoiler alert, it doesn’t look good.”

Photo made available through a Creative Commons license. This story has been changed since publication. While EutroPHIX initially used Phoslock, as we originally reported, the company (and the city) switched to lanthanum modified bentonite in 2023.

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