Effects of Exotic Floating Vegetation Control on Native Aquatic Plants in Lake Okeechobee

Late in 2018, several Florida lake users voiced concerns about herbicide use and their impact on fish, wildlife, and aquatic ecosystems. In response, FWC paused all aquatic herbicide treatments and hosted public meetings to gather input from stakeholders regarding the aquatic plant management program. Throughout 2019, FWC incorporated this input into aquatic plant management planning, with the goal of balancing public recommendations within our legislative mandate to control nuisance exotic vegetation. One change that was implemented included the designation of a no-treatment zone (approximately 500 acres) encompassing Bird Island on Lake Okeechobee. During 2020, no herbicide treatments were conducted in this designated area, which was last treated in July 2019. Researchers established study sites at Bird Island and additional study sites within a treatment zone at Second Point, near King’s Bar. Biologists will monitor the response of desirable native plants (bulrush and tape grass) in areas with and without herbicide control of exotic floating vegetation (water hyacinth and water lettuce).

Monitoring began in March 2020 and included establishing study sites within areas of bulrush and tape grass. Researchers will sample these study sites quarterly to document percent coverage of vegetation and stem density of bulrush, which can be used to indicate expansion, reduction, or no change in vegetation communities. These data will help other researchers and stakeholders understand the effects of exotic vegetation and our herbicide program on native plant communities that provide habitat benefits for fish and wildlife.

A researcher counts bulrush stems within a sampling quadrat on Lake Okeechobee (left); a bulrush study site (middle); a tape grass study site (right).