Presenter: Phil Durocher

Commission Agenda Item No. 8
Lake Conroe Hydrilla Update
November 2005

I. Executive Summary: This item presents a short history of the aquatic vegetation (hydrilla) problems experienced on Lake Conroe during the 1970's, efforts taken to address those initial problems and plans being currently formulated by the Texas Parks and Wildlife Department (TPWD) and it's partner the San Jacinto River Authority (SJRA) to address a recent outbreak of hydrilla on that reservoir.

II. Discussion: Hydrilla was first identified in Lake Conroe in 1975 only two years after the Lake was impounded. Subsequent surveys indicated hydrilla was spreading rapidly. By 1979, hydrilla had increased to over 4,500 acres and was causing significant problems for boaters, skiers, and swimmers. Coverage peeked at 8,400 acres in 1981.

As result of efforts by the Lake Conroe Association and its supporters and despite objections by TPWD staff, the Texas Legislature directed the Texas Agricultural Experiment Station and TPWD to conduct a study to determine the efficacy, and other effects of grass carp use in Lake Conroe. Between September 1981 and September 1982, 270,000 non-sterile diploid grass carp were introduced into Lake Conroe to control aquatic vegetation. By October 1983, all vegetation had been removed from the lake.

Hydrilla did not re-emerge in Lake Conroe for 13 years, but in 1996, 3.2 acres of hydrilla was discovered. For nine more years, herbicide treatments funded primarily by SJRA and conducted by SJRA and TPWD were able to successfully inhibit the expansion of hydrilla.

Despite these continued efforts, hydrilla coverage is again a concern on Lake Conroe. Coverage has increased to nearby 900 acres this summer. As a result, TPWD and SJRA have been working together to develop a comprehensive hydrilla management plan for Lake Conroe, based on the principles of Integrated Pest Management and within the scope of the TPWD State Aquatic Vegetation Management Plan. Public hearings on the plan will be held later this year. We hope to begin implementing the new plan in early 2006.