Lake Austin
About Lake Austin
A Source of Drinking Water
Lake Austin is a reservoir, one of the seven Highland Lakes, created by dams on the Colorado River. Lake Austin is relatively small and narrow, sitting between Lake Travis and Lady Bird Lake. It is a pass-through lake, meaning it does not have extra capacity to store floodwaters. It is maintained with a constant water level. It is a major source of drinking water for the City of Austin.
Lake Austin Stakeholder Group
A Lake Austin stakeholder group has been formed and will meet quarterly with City staff and subject matter experts. This group was created to bring concerns and questions from a range of stakeholders to City leadership on a regular basis.
Hydrilla Information
Vegetation on Lake Austin
In February, hydrilla was growing in approximately 37% of the lake, up from 30% in September.
Texas Parks and Wildlife conducted a survey of vegetation in Lake Austin in mid-February. They identified 592 acres of hydrilla and 58 acres of Eurasian watermilfoil.
- Hydrilla has increased from 456 acres in September while Eurasian watermilfoil has decreased from 182 acres. Overall, the footprint of invasive vegetation is up by two percent.
- Most of this shift is in the first five miles of Lake Austin below Mansfield Dam where there is a mix of the two plants. Hydrilla is now dominant in this area.
- While hydrilla is out-competing Eurasian watermilfoil, the overall footprint of invasive vegetation is similar to the fall with some increases in coves.
The map shows that the upper five miles of Lake Austin from Mansfield Dam to Lake Austin Spa has hydrilla from bank to bank. Almost all of it is submerged. This area was previously a mix of half hydrilla and half milfoil, but the milfoil has receded, and hydrilla now dominates the area.
The middle portion of the reservoir, from Commons Ford Park to Emma Long Metropolitan Park, has little hydrilla with small patches of Eurasian watermilfoil along sections of the banks.
In the lower portion of the lake between Ski Shores Café and Tom Miller Dam, hydrilla is still thick along the shoreline and out from shore approximately 100 feet. Hydrilla is also dense in backwater coves, canals, and sloughs. There are small patches of desirable native plants such as eelgrass throughout the lake. However, these plants were not surveyed in February and are not shown on the map . Filamentous green algae is growing with the hydrilla in several locations of the reservoir.
Why is Hydrilla a Problem?
In reasonable quantities, hydrilla shares some benefits with other aquatic vegetation:
- It provides oxygen for fish and other aquatic life
- It creates hiding places and forage areas for fish
- It uses up excess nutrients and absorbs other pollutants
From 1999 to 2003, hydrilla was able to cover about an eighth of the lake. We saw an even more rapid spread in the summer of 2025.
Once hydrilla covers large areas of the lake, it can cause problems for both the environment and our community. Hydrilla may form dense mats that can clog waterways. Dense mats of hydrilla can also impede boats. Hydrilla can out-compete our native vegetation.
Sterile Grass Carp
What is the City Doing?
While hydrilla supports fish habitat and water quality, it can grow so dense that it becomes a problem for the environment and the community. Managing hydrilla responsibly is a long-term effort.
Sterile grass carp have been introduced as an environmentally friendly, lake-wide, management tool because they prefer to eat hydrilla over other plants. They are stocked based on the most recent TPWD vegetation survey, past lake data, and expected climate conditions.
The “right” number of sterile grass carp is difficult to project because it requires ongoing evaluation of conditions. Based on historic Lake Austin data, about 5,000 fish appear to be a safe quantity as long as there is enough hydrilla in the lake for them to eat. Future conditions can change quickly, so stocking decisions must be based on the latest data.
An additional 2,790 sterile grass carp will be stocked into Lake Austin in early May to help manage hydrilla. They will be released near Tom Miller and Mansfield Dams. This will bring the population of grass carp in Lake Austin up from 5 fish per acre to 8 fish per acre of hydrilla.
We do not expect to see immediate reductions in the amount of hydrilla after the grass carp are stocked. However, we expect to make sustained progress on managing hydrilla over time.
Why Are Other Options Limited?
Historically, drawdowns on Lake Austin were done in winter. LCRA guidance now does not allow drawdowns on the Highland Lakes during winter or summer because of the need to maintain reliable hydroelectric power generation during those months. Lowering the lake in the spring would harm fish because they spawn in shallow water during the spring. Spring storms can also create safety and erosion risks when the lake bed is exposed. The root systems of hydrilla survive lake drawdowns, and the plant may bounce back within a short time.
Herbicides are not allowed for use in Lake Austin. While some other Texas lakes use aquatic herbicides, Lake Austin is a relatively small, narrow reservoir with dense residential shoreline development and supplies two of Austin’s major drinking water treatment plants, in addition to other smaller-scale water treatment plants in the area, and some private shoreline residences. Chemicals placed in one area can move downstream and be drawn into public drinking water intakes and/or private intakes for potable and landscaping uses.
Mechanical removal is the recommended method for shoreline homeowners to get temporary, localized relief. Mechanical removal on a lake-wide scale is not feasible due to the speed at which hydrilla grows and its ability to regrow from small pieces.
If manually removing or raking hydrilla from your shoreline, make sure it is properly disposed of or composted.
Historical Information
A Balancing Act
Managing hydrilla with sterile grass carp is a complicated balancing act that takes time. Grass carp generally live for 10 to 20 years, but some may live longer. They prefer to eat hydrilla over other vegetation.
On one hand, it takes time for them to eat enough hydrilla to have a visible impact. On the other hand, there needs to be enough food for them for their whole lifecycle. We do not expect to see immediate reductions in the amount of hydrilla after the grass carp are stocked. However, we expect to make sustained progress on managing hydrilla over time.
Past experience shows that environmental conditions can also have a significant impact on the spread of hydrilla. Droughts create conditions favorable to hydrilla. During the drought from 2010 to 2013, it seemed like we couldn’t stock enough grass carp to keep hydrilla under control. But once the drought ended, the grass carp were still around. Beginning around 2014, all aquatic vegetation began disappearing from the lake, eaten by hungry grass carp. It has taken about 10 years for the lake to recover and reach target levels of aquatic vegetation.
Environmental factors may have contributed to the rapid spread of hydrilla in 2025. We think it may be a combination of flooding and drought. The July floods may have brought in more sediments and nutrients. But, since the floodwaters were stored in upstream lakes, flows through Lake Austin were not fast enough to uproot the hydrilla as previous floods have done. The added nutrients from the July floods may have combined with warm waters and low flows to create the perfect growing conditions for hydrilla. Rain from a number of smaller storms may also have washed fertilizers from shoreline lawns into the lake.
Past experiences underlines the importance of proceeding with caution and giving the lake environment time to adjust to changing conditions. Our goal is to avoid harming wildlife habitat or water quality to ensure a healthy lake for the environment and the community.
This graph compares the amount of vegetation in Lake Austin, the number of sterile grass carp stocked in the lake, and periods of drought.
Properties on the Lake
Fertilizers used on lawns and gardens may be washed into the lake when it rains and contribute to the growth of hydrilla. Consider reducing the use of fertilizers on lawns. In addition, creating a landscaped area with native and adapted plants along the shoreline may help. The plants act as a buffer and help prevent nutrients and other pollutants from entering the lake.
If you are struggling with hydrilla near your property, consider hiring a contractor to clear the hydrilla around docks. The contractor should have a permit from the Texas Parks and Wildlife Department to perform this work.
- Get information about sustainable landscaping at GrowGreen
- Get information about nuisance aquatic vegetation from Texas Parks and Wildlife
How Can I Help?
In addition to avoiding the use of fertilizers, residents and visitors can take the following steps to help prevent the spread of non-native species, like hydrilla:
- Clean, drain, and dry your boat, trailer, and gear before and after use;
- Avoid swimming and boating through dense patches of underwater vegetation;
- If manually removing or raking hydrilla from your shoreline, make sure it is properly disposed of or composted.
More Information
We monitor the water quality in our lakes and creeks in order to understand how the urban environment affects our water bodies and to develop effective policies to protect them.
The State of Our Environment Report includes the most recent monitoring data for our lakes, creeks and aquifers.
Real-time river and lake conditions, weather radar and more.
We monitor the water quality in our lakes and creeks in order to understand how the urban environment affects our water bodies and to develop effective policies to protect them.
The State of Our Environment Report includes the most recent monitoring data for our lakes, creeks and aquifers.
Real-time river and lake conditions, weather radar and more.
Our creeks and lakes are home to an amazing number of trees, birds, fish, and other wildlife.
Austin’s waterways are home to many different types of algae that play important roles in the natural world.
LCRA produces electric power, manages the lower Colorado River, provides water, manages a public parks system and supports community development.