Presenter: Phil Durocher

Commission Agenda Item No. 9
Aquatic Vegetation Management – Lake Austin Update
January 2004

I. Executive Summary: This item apprises the Commission on actions taken by TPWD and local cooperators to control the submerged aquatic weed hydrilla (Hydrilla verticillata) in Lake Austin.

II. Discussion: In 1999, 23 acres of hydrilla, a prohibited aquatic weed in Texas, was discovered in Lake Austin. Because of its rapid growth rate and invasiveness, hydrilla has become problematic in many U.S. lakes, including a number in Texas. TPWD personnel began meeting with the Lower Colorado River Authority (LCRA) and the City of Austin to determine possible management options. Problems associated with management and control techniques slowed the development of a plan and hydrilla continued to spread in the Lake, peaking at 320 acres in 2002. By the fall of 2002 the Lake Austin Hydrilla Management Plan 2002-2003, based on the principles of Integrated Pest Management, was finalized by TPWD, LCRA, the City of Austin, and the Friends of Lake Austin. The objectives of the plan were 1) to return Lake Austin to pre-hydrilla conditions and 2) to maintain a healthy lake ecosystem and fishery in the lake. Management/control measures in the plan included the use of mechanical harvest, herbicide treatment, and sterile triploid grass carp. During 2003, in an effort to minimize the risk of overstocking, the City of Austin conducted four incremental triploid grass carp stockings. The number of fish stocked each time was based on TPWD vegetation surveys. To date the total number of grass carp stocked has been 3,825. During the 2003 summer recreational season, hydrilla was much less problematic than it had been in recent years. However, vegetation surveys conducted during 2003 revealed hydrilla has continued to spread to new areas and the City of Austin has been authorized to stock up to 2,575 more triploid grass carp in Lake Austin. Currently, a new Lake Austin Hydrilla Management Plan is being developed for 2004.