Lake level critical to improving aquatic vegetation

OKEECHOBEE — Maintaining the lake level below 15.5 ft. is key to restoring native aquatic plants in Lake Okeechobee according to a Florida Fish and Wildlife Commission (FWC) report given at the Nov. 8 meeting of the Okeechobee County Board of Commissioners.That’s the message local officials hope to spread statewide.

At the Nov. 8, 2018 meeting of the Okeechobee County Commission, Mariah McInnis, of FWC, shared this 2013 image of aquatic plants in the Monkey Box on Lake Okeechobee. She said without chemical spraying, nonnative plants will grow quickly into large mats that impede navigation, block sunlight from the water column and crowd out native vegetation.

“We need to be very clear about where the lake level needs to be for the native vegetation to thrive,” said Commissioner Kelly Owens.

Mariah McInnis, of FWC, provided the board with information on the use of chemical herbicides for aquatic plant management on the lake. She said the aquatic spraying is sometimes blamed for the loss of aquatic vegetation in Lake Okeechobee, but the real threat to the native vegetation has to do with lake levels.

“There has been a significant loss of submerged vegetation,” she said. “This was caused by high water events that have deprived the plants of sunlight.”

She said turbulent conditions also damage aquatic plants and when the lake it deeper, there is more turbulence.

“More water, more wave action,” she said.

The ideal water level is 12.5 to 15 ft., she said. High water events are harmful to lake vegetation.

The lake lost thousands and thousands of acres of submerged vegetation in Lake Okeechobee due to the deep water levels in 2016 and 2017, she said.

Another issue, she said is the high nutrient load in the water entering the lake.

In the last water year, 1,000 metric tons of phosphorus flowed into Lake Okeechobee; Florida Department of Environmental Protection has set the target limit for phosphorus at 105 metric tons a year (plus 35 metric tons from atmospheric loading).

Because Lake Okeechobee has a heavy influx of nutrients in the water flowing into the lake, some of the plants grow very quickly. In some cases, even native plants can grow so rapidly that they become a hindrance to navigation.

In some cases cattails, which are native, become so thick they become a problem and are treated on a case-by-case basis, Ma. McInnis said.

Water lettuce and water hyacinth are treated pretty much year round on Lake Okeechobee, she explained. She said these are non-native plants, although water lettuce was documented in Florida as early as 1765.

Ms. McInnis said left unchecked, these floating plants create mats so dense they block out sunlight and reduce the oxygen in the water. They also provide prime habitat for mosquitoes to breed.

She said she creates a weekly spraying schedule based on observations by airboat and helicopter.

“Our applicators use a variety of herbicide that are each used in different situations. Some of these are highly selective and we actually use the highly selective ones the most often,” she said.

Work is assessed post treatment, Ms. McInnis continued.

“Part of my job, when I go out on my airboat surveys, I am assessing post treatment,” she explained.

FWC uses three different contractors on the lake right now: Applied Aquatic, AVC and Lake and Wetland, she explained. They are divided into regions.

Work is assigned weekly and is publicly available, she said.

“They send me their GPS tracks weekly,” she said.

Contractors have to be licensed by Florida Department of Agriculture and Consumer Services and must complete additional training annually.

Applicators are paid hourly not by the amount of herbicide used, she said. “There is no incentive for them to dump chemicals.

“I believe our contractors are trained and skilled and have every tool to get the job done well, but they are human and are not exempt from humor error,” she said.

She said she encourages anyone who sees a problem with spraying of aquatic vegetation to take photos and/or video and contact her at 352-601-1367.

She said they are working with stakeholders to try to limit spraying in critical areas during spawning season.

“Sometimes there are tournaments on the lake and anglers are aggravated when right before the tournament they spray a key area where fish were being caught,” said Commissioner Owens.

Ms. McInnis said they are also willing to work with the tourism board to prevent spraying in designated areas right before a large bass tournament.

An earlier article in the Okeechobee News is available with photos of the various friendly and not-so-friendly plants. Click here.

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