On Tuesday, November 6, 2012, 6,000 sterile Asian grass carp will be released into Lake Austin as part of the ongoing effort to control the invasive, exotic weed hydrilla. This stocking is intended to replace fish lost to natural mortality to maintain a target population of 50 fish per acre of hydrilla, a rate that has controlled hydrilla in the past.

For several years, hydrilla has covered less than 80 acres of Lake Austin, held in check primarily by the periodic stocking of sterile Asian grass carp. The fish were part of an integrated hydrilla management plan developed in partnership with the City of Austin, Texas Parks and Wildlife Department (TPWD), Lower Colorado River Authority and the citizen group, Friends of Lake Austin.

During 2011, hydrilla began to increase, reaching a historic high of 580 acres in July 2012, according to a TPWD vegetation survey.  

This increase is likely due to the ongoing drought, which created conditions favoring hydrilla over other aquatic vegetation. In particular, hydrilla prefers the much warmer water flowing into Lake Austin from drought-stricken Lake Travis. Releases from Lake Travis for downstream irrigation have also decreased this year, limiting the water flowing through Lake Austin and contributing to hydrilla growth.

Find out more on the Hydrilla web page.

In response to this significant increase, more than 11,000 fish were stocked this summer, bringing the total number of fish stocked to over 40,000. TPWD documented that hydrilla coverage decreased slightly to 560 acres in September.