Optimism about eradicating hydrilla and stopping its spread is based on success in other parts of the country. Professionals in California and elsewhere have been generous in sharing their knowledge and experience, which we have used in formulating plans to help other communities fight this aggressive weed.
Hydrilla was first found in California in a man-made lake in 1976, and surveys began the following year. In 1985, hydrilla was found in a second location, and the Governor of California declared a "State of Emergency". Eradication strategies included manual removal, small scale dredging, lining of water bodies with cement, biological control, and aquatic herbicides. Of the 29 separate waterbodies in which hydrilla was discovered, it has been eradicated from 20 of them by the Hydrilla Eradication program, which continues to work to eradicate hydrilla from 9 remaining locations. Herbicide treatments of the affected areas continued for three growing seasons after the last hydrilla detection, and surveys continue in those areas for at least the following three years.
More information about the specific herbicides used can be found on Page 5 of the report. Page 8 of the report provides the status of infestations in California by county, and detailed descriptions of eradication projects are provided starting on Page 10.
The Clear Lake eradication effort is described on pages 15-26 and shows how persistent hydrilla can be, while giving an example of a coordinated effort against a local hydrilla infestation.
Hydrilla was discovered in Pipe Lake and Lake Lucerne in 1994, and immediate eradication efforts in both lakes were organized by the Washington State Department of Ecology. Hand pulling, whole lake herbicide treatments, and spot treatments were employed, and in 2003 the combination of surveys and herbicide treatment finally had a significant impact on the hydrilla population. By 2009, hydrilla had been absent from Pipe Lake for three years and from Lake Lucerne for five years. 2009 marked the seventh year of using an eradication method that involved the use of slow release herbicide as well as frequent diver and snorkel assessments.
Comprehensive plant surveys began in 2010 after the herbicide treatments were ceased to ensure the treatment was completely effective, and will continue to monitor the regrowth of native plants. The total cost of the eradication program in King County was $61,131.65, of which $55,020.46 was considered eligible for grant reimbursal.
Pipe and Lucerne Lakes 2009 Hydrilla Eradication Project: Annual Report. Washington State Department of Ecology, Water Quality Program. 2010
Update January 2013 from a King County WA aquatic weed specialist about Pipe and Lucerne Lakes: they are still hydrilla free (last seen in 2006) and will be monitored annually by divers until 2014.
Last updated July 26, 2019