City considers first Lake Austin drawdown since 2017 amid hydrilla concerns

The city of Austin could lower Lake Austin for the first time in nearly a decade this fall - but city officials remain unconvinced that drawing down the lake would help control an infestation of invasive hydrilla that plagues the waterway.

Austin Water is expected to decide within the next month whether it will lower lake levels by 10 to 12 feet in October at the request of shoreline stakeholders, the utility said in a statement Monday.

Lowering the lake would "give access to private property owners for dock and bulkhead maintenance, debris and sediment removal, and may also temporarily help manage nuisance aquatic vegetation," the statement reads. The drawdown would take place over six weeks in October and November.

Operators have historically lowered Lake Austin every two years or so, barring drought. But this fall's drawdown would be the first since 2017 if city leaders and the Lower Colorado River Authority - which operates the hydroelectric dams on both ends of the lake - approve it.

The nearly decade-long hiatus was due largely to prolonged drought conditions, Austin Water engineer Teresa Lutes recently told a City Council committee. She said that, moving forward, the city plans to lower the lake about every four years.

Lake Austin has hovered at roughly 97% full over the past year.

The proposed drawdown was requested last year by a group of shoreline property owners, according to an October memo from Austin Water and Austin Watershed Protection. Besides granting easier access for maintenance, the property owners hope lowering the lake will kill off some of the invasive vegetation near the shoreline and facilitate its removal.

More than 40% of the lake is infested with hydrilla and Eurasian watermilfoil, another invasive plant, according to a Monday memo from Austin Watershed Protection. Hydrilla grows quickly and can "form dense mats that can clog waterways and impede navigation, posing a nuisance to boaters,

swimmers, and other recreational users," the memo reads. It was first found in Lake Austin in 1999.

Though drawing down the lake could lead to a temporary reduction in the nuisance plant, city staff have said it won't have much impact in the long-term and could even encourage it to sprout.

"A review of historical data from 1999 to 2025, including Texas Parks and Wildlife Department vegetation surveys, indicates that drawdowns are not effective at controlling hydrilla," the October memo reads. "Data suggests drawdowns may have the opposite effect, facilitating hydrilla's growth by reducing competition from other aquatic plants in shallow areas."

Instead, Austin Watershed Protection plans to fight fire with fire, introducing additional nonnative grass carp to eat the invasive vegetation.The carp, which will eat just about any leafy aquatic vegetation in their path, were first stocked at Lake Austin in 2003 in an effort to control hydrilla. The fish are sterile, so they can't reproduce.

Austin Watershed Protection has stocked about 5,000 grass carp in Lake Austin since last July, and plans to stock more this fall. The key is not to overdo it, the Monday memo states, since having too many of the fish in the lake would devastate native vegetation and negatively affect aquatic habitats. City scientists learned this lesson firsthand in the 2010s.

"Overstocking grass carp in response to rapid growth and spread of hydrilla resulted in the elimination of all aquatic vegetation, a condition that persisted for nearly a decade," staff wrote. "This elimination of all aquatic vegetation caused a cascade of negative effects, including increased planktonic algae blooms and a lack of habitat, leading to a collapse of the fishery and poorer overall water quality."

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