Henderson Lake drawdown planned

Another drawdown of Henderson Lake is just weeks away. At the July 5 St. Martin Parish Council meeting, Louisiana Department of Wildlife and Fisheries Biologist Manager Brac Salyers delivered a presentation on the process and the necessity of the action.

Salyers reported that the mild 2021-22 winter has allowed the lake’s three main types of nuisance vegetation to thrive. Hydrilla, water hyacinth and giant salvinia all threaten to choke off lake access and stress fish stocks if control measures are not taken at the appropriate time.

That time is approaching, and the drawdown will begin in early August, Salyers said. The Henderson Control Structure will be opened in a controlled manner to drop the level by three inches per day. The current lake level of nine feet will be reduced to six feet and will be kept at that level until early November.

In recent years, Salyers explained, high rainfall events such as the August 2016 flood  have come just at the time the drawdown was being attempted. The past three drawdowns have been ineffective because rainfall prevented the target levels from being reached.

Herbicide spraying and other control measures work in conjunction with the drawdown to fight back the invasive plants. Unchecked, giant salvinia, which was first detected in the lake in 2012,  can double in mass every three to four day and will continue to grow until the entire water body is covered with an impassable six-foot-deep mat.

Other measures include introducing salvinia-eating beetles. The beetles do not spread widely on their own, so populations of the insects have to be gathered and  introduced to other salvinia-plagued areas in the lake.

Hydrilla has also been an increasing problem in South Louisiana and, unchecked, can make the lake nearly unusable. Hydrilla covered an estimated 2,500 acres, or about 50 percent, of the lake in 2014. 

Water hyacinths, like hydrilla, must be controlled with herbicide and about 3,400 acres of hyacinth are sprayed annually. 

The severity of the overgrown vegetation problem was brought home recently when a group of Scouts on one of the Swamp Base Adventure excursions  became stranded by giant salvinia and had to be rescued.

Parish President Chester Cedars interjected that, during the drawdown period, lake use is not prohibited, but the low water level will limit access throughout the period. Salyers pointed out, however, that the drawdown is essential for both vegetation control and habitat improvement that will result in better fish populations.

The low water level causes the lake bottom to compact, which allows more eggs and hatchlings of nesting fish species, including  bass, crappie and bluegill to survive. The sacrifice of fishing opportunities now will pay off later with better catches as well as improved boat lanes in the lake, Salyers concluded.

In other business, the council approved:

•An ordinance providing for the levying of the voter-approved one percent sales tax in Sales Tax District One. 

•An ordinance providing for the sale of the final $10 million in general obligation bonds earmarked for drainage projects, which was approved by voters in 2016.

•A certificate of substantial completion for the Bayou Benoit boat landing improvement project.