Floating phosphorus sponges may help clear up Hayden Lake

A Hayden Lake homeowners association installed a floating wetland next to its community dock Thursday, with the goal of improving water quality in one of the lake’s murky bays.

Water sedges, monkey flowers and nutrient-loving grasses sprouted from two rafts constructed from spongy, plastic membranes. As the plants grow, their roots will form a thick mat that sucks phosphorus out of the bay.

“They’re basically growing like hydroponics,” said Karen Hayes, who is part of the Kootenai Environmental Alliance’s Hayden Lake Project.

KEA is looking for ways to improve water quality in the lake, which has exceeded federal water quality limits for phosphorus since the late 1990s.

Adrienne Cronebaugh, KEA’s executive director, said the floating wetlands could be a partial solution to the problem of excess nutrients in the lake, which has been affected by rapid residential development as well as past logging and farming.

KEA used grant money to purchase the two floating wetlands, each about 70 square feet. The wetlands are made by Floating Island International, a Montana company that sells them for about $30 per square foot.

KEA piloted the floating wetland concept two years ago on a 1-acre private pond in the Hayden Lake watershed. North Idaho College students tracked water quality in the pond, documenting decreases in phosphorus levels and coliform bacteria. The pond’s pH also improved after the floating wetlands were installed, with the water becoming less acidic.

When the organization was ready to launch the wetlands in the lake, it chose McLeans Bay for the demonstration site. The bay’s water quality will be tracked for five years to evaluate the floating wetlands’ effectiveness.

The 25-acre bay on the north side of the lake is “a perfect petri dish” for the project, said Diane Lawrence, who belongs to the McCauley Emerald Homeowners Association, which has been working cooperatively with KEA.

Water lilies often cover the shallow bay, and underwater weeds are a problem for boaters.

“A couple of summers ago, the clarity of the bay was horrible,” Lawrence said. “We had trouble backing the boats out, the vegetation was so intense.”

A neighbor who had a Jet Ski ended up selling it because the intake was constantly choked with weeds, said Lawrence’s husband, Tom.

Protecting the lake’s water quality is good for property values, the couple said, but the issue is multifaceted. Nutrients enter the lake through a variety of sources, including erosion, fertilizers and runoff from residential construction.

Better development standards are helping address runoff, Tom Lawrence said. Residents also need to know how their actions affect Hayden Lake’s water quality, he added. Fertilizing lawns and using phosphorus-rich soaps contribute to the nutrient load.

Meanwhile, the floating wetlands have attracted interest from homeowners associations in other bays. Diane Lawrence can picture them taking off on Hayden Lake.

On other lakes, the floating wetlands have been planted with flowers or vegetables.

They’re safe from hungry deer, and they don’t require watering, Diane Lawrence said.