Controlling aquatic vegetation

Wednesday, August 15, 2018
Employees from Mammoth Spring State Park work to control aquatic vegetation that has a negative impact on the lake.
Renee Janes

The lake at Mammoth Spring State Park is a main attraction to the area, however, employees with the park have an ongoing battle with controlling the aquatic vegetation that grows in it.

On Wednesday, Aug. 8, employees from the park attempted to mechanically remove aquatic vegetation or lake weeds with the use of their john boat by attaching a rebar rake to the front and catching the weeds on the tines, which are then carried off in the current.

Mammoth Spring Park Superintendent Dave Jackson stated they donít remove a lot at a time for two reasons. One is because fishermen donít like the vegetation floating around their legs when standing in the water. Another reason is to keep it from plugging the screens at Dam 3.

So far this year, they have only used the john boat to clear vegetation for three hours. Two reasons this is done is because of complaints received of the lake looking like a lagoon or it smells; and because the vegetation effects the operation of paddle boats and kayaks, causing them to get stuck. Then boats must be pulled out of the vegetation.

It also extends the season for boats to be rented, so they may be rented up until the end of August and sometimes through the month of September.

The number of times the lake requires cleaning is different every year. The main control method used to control the vegetation is the winter drawdown in which the lake level is lowered in January and February to freeze the aquatic vegetation. It helps to stunt the growth. However, it still comes back. If this is not done, the vegetation growth will be bad by the time June rolls around. This raises the possibility of not renting boats by July.

Jackson stated one solution would be for the lake to be dredged deeper, but this would cost more than $1 million.

The park has occasionally used EPA approved chemicals in the lake, but they are temporary solutions to the problem. They have used aquacide pellets, which are distributed into the lake and absorbs into the plants, killing them at the root. However, because of the dilution rate and moving water, the contact with the plant is lessened and isnít sufficiently absorbed.

Another method tried previously was to spray a chemical on the vegetation. Jackson stated they had not tried it for a few years as upon contact with water it becomes inert and only works on vegetation above water.

Jackson stated these donít harm wildlife but are also not effective.

The park previously also had an aquatic weed harvester cut the vegetation. However, this was not a solution. Jackson explained, they use a mechanical boat that cuts weeds to a depth of approximately six feet, but it makes it grow back thicker. The boat was borrowed from the Corps of Engineers, but is unavailable because it was transferred.

The types of vegetation changes every year. For instance, a dominant vegetation one year, may be eradicated and another kind take over.

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