Green Valley Lake An 'Interesting Beast To Manage'

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This time of year, the summer heat and sun set off a cycle of algae growth in the lakes of Green Valley Park and with it a cycle of complaints to the Payson Park and Recreation Department.

In response, the town dredges the lake in an attempt to keep the water relatively clear.

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Scott Kelly, water department operator, drives a boat designed to dredge weeds. With this pontoon tractor, not only can he give the lake a better visual appearance, but with the weeds, out come the attached nutrients that feed algae.

But algae is part of the cycle of life in any lake bottom that sunlight penetrates. Green Valley Park is not exempt from this natural photosynthetic process.

Algae is a seasonal phenomenon. Different types bloom in different seasons. The hot summer sun causes the most growth.

"Depending on what is going on in the lake we treat (the water) starting in springtime, through the summer and sometimes into the fall," said water quality specialist for the town, Karen Probert.

The lake is monitored year-round. Every lake's biology is different and even with careful monitoring, unexpected algae can grow.

Rainfall and unseasonable heat affects lakes.

So does nutrient content.

A 10-pound Canada goose can produce four pounds of nitrate and phosphate rich waste per day.

New species of algae come in on boats that have been in the waters of different lakes.

"Sometime Game and Fish will issue alerts to warn people to take all the vegetation off their boats before they go into new water because different types of organisms and parasites can be transferred that way," Probert said.

GVP was designed for ground water recharge. Recreational uses are secondary.

From a recreational standpoint, water in the lake is best from September of one year through spring of the next.

"One of the things we found initially when the GVP lakes were first put in operation is that there were a lot of bad sulfur odors because we were losing oxygen at the bottom of the lake," Probert said.

An aeration system cleared the problem.

"The water percolates through the bottom of the lake and it soaks back into the groundwater. Then when we pump our wells, the water is drawn from the aquifer and used as drinking water," Probert said. "We want to do everything we can to protect our drinking water quality.

"The whole design of GVP was to be able to take this treated effluent, put it in the lake and use it for landscape irrigation around town but also have the benefit of recharging the aquifer through that percolation process."

Chemicals could be added to the water to make it crystal clear and people could see to the bottom of its 22-foot center depth.

But then there wouldn't be any fish and the chemicals would pollute the drinking water and create bigger problems.

Several other methods for controlling algae at Green Valley Park have been tested on the lakes including a light inhibiting dye designed to limit photosynthesis, but because the water is moving the dye diluted too fast to be cost-effective.

"(The lake) is an interesting beast to try to manage," said Parks and Recreation director Bill Schwind.

Bacteria and enzymes the town is now using to treat the water at GVP is intended to reduce the nutrient that cause algae to grow and also prevents sludge from forming at the bottom of the lake, clogging the aeration system.

Currently, according to Probert, the sanitary district puts a BioBrick restriction enzyme in the water. The lake is also treated with a biological product to deter mosquitoes.

Any biological products are augmented with muscle.

"The staff (at the water department) took the pontoon boat we already had and some surplus tractor equipment and made a weed harvester that has been really successful," Probert said.

It cost a couple thousand dollars to build the harvester. A similar machine that would not have done the job nearly as well would have cost $60,000.

Adding grass eating carp and bottom feeding catfish to the lake is a possibility that is further down the road, Schwind said. The fish are not native species to area waterways so the Game and Fish would have to approve their introduction.

"We're just trying to figure out how to help this patient of ours that this time of year gets a little green," Schwind said.

-- To reach Carol La Valley call 474-5251 ext. 122 or e-mail clavalley@payson.com.

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