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Frequently Asked Questions

All three lakes are manmade reservoirs, Lady Bird and Lake Austin are flow-through reservoirs on the Colorado River, and Lake Long is a cooling reservoir for the Decker Creek Power Station.

Lady Bird 471 surface acres, 5 miles long Created in 1960 as an impoundment of the Colorado River with the completion of Longhorn Dam Originally named Town Lake, renamed Lady Bird Lake in 2007 to honor Lady Bird Johnson Operation and flow Flow-through reservoir (little storage capacity), typically has two ‘seasons’

  •  Mar-Oct has higher flows, more river-like as LCRA passes water through to downstream rice farmers
  • Oct- Mar has lower flows, more lake-like as water is stored in Lake Travis for use during irrigation season

Beginning in 2012, the flows became less variable, as LCRA has restricted irrigation releases during the historic drought.

Reservoir uses

Lady Bird used to be a source of public drinking water and also was a cooling reservoir for the now-decommissioned Holly Power Plant (Future:  Holly Shores project) Currently, the lake is primarily used for non-motorized recreation (canoeing, kayaking, competitive rowing, paddleboarding) as well as providing refuge for a wide variety of birds and urban wildlife. It is also a great spot for fishing, whether from the shore or on the water (gas motors  on your boat! Check out TPWD’s web for more details Lady Bird’s Hike and Bike Trail.

Lady Bird's Hike and Bike Trail is an important recreational ‘get away’ for both Austinites and visitors.

Lake Austin

1600 surface acres 21 miles long Created in 1940 as an impoundment of the Colorado River with the completion of Tom Miller Dam Operation and flow Flow-through reservoir with little storage capacity, typically has two ‘seasons’:

  • Mar-Oct has higher flows, more river-like as LCRA passes water through to downstream rice farmers 
  • Oct- Mar has lower flows, more lake-like as water is stored in Lake Travis for use during irrigation season In 2012, the flows became less variable, as LCRA has restricted irrigation releases during the historic drought.

Reservoir uses

Current uses include generation of hydroelectric power at upper (Mansfield) and lower (Tom Miller) dams, conveyance of flood and irrigation water, multiple public and private drinking water intakes, including two owned by City of Austin (Ullrich and Davis Water Treatment Plants). Several parks and public boat ramps provide public access, check this link for more information.

Important recreation destination for water sports and sport fishing, with trophy sized large mouth bass. For more information on fishing Lake Austin, check TPWD’s webpage.

Lake Walter E. Long 1,269 surface acres Created in 1967 as a cooling reservoir for Decker Creek Power Station, it impounds Decker Creek. City of Austin owns the lake and entire shoreline Public access (park and boat ramp) on the southeast shore, click here for more details  Insert link to PARD Lake Long site: http://www.austintexas.gov/page/lake-walter-e-long

Important recreational resource, Walter E. Long Park (link) with healthy sport fish communities. . For more information about fishing at Lake Long, check TPWD’s webpage.

Operations and flow: Up to 680 million gallons of water per day is pulled in from the Colorado River to the southwestern arm of the reservoir and used as cooling water for the power plant.  This warmer water is discharged into the northeast arm, losing heat as it flows through the reservoir, back to the southwest area. The lake level is maintained by pumping water from the Colorado River at an average rate of 16,156 acre feet/year.  Austin Energy then releases 500 gallons per day to maintain flow through the lake and in Decker Creek downstream of the lake.  Lake water quality: This river water is high in nutrients, and this combines with the warm water from the power plant to limit the lake’s water quality, regardless of the healthy riparian zone provided by the preserve and parkland along its shores. The increased nutrients, warmer water temps and longer retention time often leave the lake vulnerable to algal blooms through out the year.  

There are six categories of data collected and used to calculate sub index scores:

  1. Water Quality

Collected at the surface and bottom of the lake

  • Nutrients (Nitrate-N, Ammonia-N, and Orthophosphorus)

Collected only at the surface

  • Total Suspended Solids
  • E coli bacteria

Collected along a depth profile

  • Conductivity
  • pH, temperature and dissolved oxygen are also collected but are not part of scoring

2. Sediment Quality
Sediment Chemistry

  • Sampled at the deepest point of each lake near the lower dam.
  • Shows the accumulation of material from the lake’s watershed
  • Metals, PAHs, pesticides and herbicides

3. Habitat Quality-
Visual assessment based on EMAP protocol

  • Riparian zone plant density, community structure, and width
  • Shoreline characteristics
  • Aquatic cover and substrate characteristics

4. Aquatic Life
Benthic Macroinvertebrate Community

  • 7 metrics assessing: Diversity, Pollution Tolerance, and Community Structure
  • Evaluates lake health beyond single ‘snapshot’ of water chemistry sample

5. Vegetation
Surveys performed by Texas Parks and Wildlife Department

  • 3 metrics assessing: Percent coverage, Diversity, and Community Structure, including invasive species cover
  • Total acreage of all plant species

6. Eutrophication
Phytoplankton community

      • 3 metrics assessing: Phytoplankton abundance, Pollution Tolerance, and Community Structure
      • Evaluates lake health and nutrient loading beyond single ‘snapshot’ of water chemistry sample

A more complete description of the parameters and methods are provided in the Lake Index Methodology.

Where on each lake is data collected?
For all lakes:
Sediment is collected from the substrate at the bottom of the lake near the downstream dam on each lake
Habitat data are collected at 10 evenly spaced sites throughout the lake
Benthic macroinvertebrates (Aquatic Life score) are collected in shallow water at 3,5, and 6 of the 10 habitat sites on Lady Bird Lake, Lake Austin, and Lake Long respectively.
Vegetation scores are based on TPWD surveys that map all the aquatic plants in each lake
Water quality and phytoplankton (Eutrophication score) samples are collected at the surface and bottom at 3 sites on each lake:
Lady Bird Lake
Near Longhorn Dam in the Basin
Downstream of 1st Street
Downstream of Redbud Isle
Lake Austin
Near Tom Miller Dam
Emma Long Metropolitan (City) Park
Low Water bridge
Lake Long
SW arm
NE arm
Near the dam

A general summary of current scores on each lake can be accessed at the Watershed Fact Sheets for Lady Bird Lake, Lake Austin, and Lake Long.

Raw data collected from each lake can be found on DataMart.

Lady Bird Lake

Lake Long

Lake Austin

DataMart