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Officials recommend managed drawdown of Anderson/Henderson Lake to fight invasive plants
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Summary
A parish presentation called for a controlled drawdown from 9 to 6 feet over about two weeks to strand invasive hydrilla, water hyacinth and giant salvinia; speakers cited heavy infestations, prior 2014 success after an Army Corps permit and rising herbicide costs.
An unidentified presenter told the St. Martin Parish council that Anderson (Henderson) Lake faces a severe infestation of invasive aquatic plants and recommended a managed drawdown to reduce the growth and reproduction of those species.
“The biggest reason is we have a severe aquatic, a chronic, aquatic plant problem on Anderson Lake,” the presenter said, listing hydrilla, water hyacinth and giant salvinia as the primary invaders. He said the lake is roughly 5,000 acres at full pool and that a 2014 survey showed about 2,500 acres—roughly 50 percent—covered by invasive plants.
The presenter outlined an integrated control strategy that combines biological controls (stocking grass carp and releasing specialist weevils), mechanical work and targeted chemical treatments. He said parish releases have included about 53,000 grass carp over a five‑year period and approximately 300,000 specialist weevils over 13 years. He added that chemical control has been expensive this season: “Just this year alone... we’ve spent almost a $150,000,” the presenter said.
As an alternative to relying solely on contractors and herbicide, the presenter recommended a managed drawdown: lowering the lake from the pool stage at 9 feet to 6 feet at a slow rate—about 2 to 4 inches per day—so rooted and floating plants become stranded, exposed to sunlight and die. “The reason we go slow... is because the summer is the hottest months,” he said, explaining the need to avoid fish kills caused by rapid oxygen loss.
The presenter noted additional benefits: the drawdown would allow safer access to inspect and repair the lake’s water‑control structure, and repeat drawdown cycles over several years (research cited by the presenter suggests 3–5 years) are likely needed to maintain control.
Council members and staff discussed operational constraints. Parish staff noted they no longer maintain a full in‑house spray crew and have contracted work to private firms; fiscal and staffing limits were cited as reasons for past downsizing. The presenter and staff emphasized that drawdowns are not always successful—high river stages, mechanical issues with structures and environmental conditions can prevent or reverse the benefit.
Next steps identified at the meeting included confirming permitting requirements (the presenter said the parish obtained an Army Corps permit for a drawdown in 2014), estimating total costs for a drawdown plus follow‑up contracts, and coordinating scheduling to avoid adverse impacts to small businesses that use private boat ramps. Parish staff and council members requested follow‑up materials: a permit/status update, cost estimates for a managed drawdown, and a plan for worker/contractor access to the control structure.
