The thick layer of weeds on Monona Bay is being challenged again this year by floating water circulators that are supposed to help clear the water.

The city of Madison agreed to pay about $75,000 to rent the SolarBees for the current growing season, after using them in a free trial year.

"We're renting them for one year, because one year of data makes it hard to tell if they're having an impact on the algae and weeds. The data was inconclusive last year," said Genesis Bichanich, a water resource specialist with the city of Madison's engineering department.

If they appear to work, the city could decide to purchase them for $225,000. However, 60 percent of this year's rental fee could be applied to the purchase price.

Five of the SolarBees are in Monona Bay and a sixth one is in a triangle formed by the railroad trestle and the bridge over John Nolen Drive. They were put into the lake on May 18. "The weeds are so thick, they're just a blanket out there," Bichanich said. "It's curly leaf pond weed, and harvesters are cutting it now."

The floating water circulators are touted to eliminate nasty algae blooms, improve water quality and reduce weeds. The 16-foot-wide, solar-powered machines are designed to attack blue-green algae by circulating water and disrupting the habitat, company limnologists say. Each machine sucks water from the bottom of the lake up through a tube and distributes it on the surface over an area of up to 50 acres.

- Brenda Ingersoll

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