The controversial solar devices used for the past two years in an effort to control weeds on Monona Bay won't be returning next year.

"There just wasn't any evidence the SolarBees were doing anything for us," said Genesis Bichanich, a water resource specialist with the city of Madison's engineering department.

The city first used the floating water circulators in a free trial in 2005, but data on their effectiveness was inconclusive, Bichanich said. This year, the city rented the devices for about $75,000, and could have applied 60 percent of the rental fee to the $225,000 cost of purchasing them.

Five SolarBees were placed in Monona Bay, and a sixth one was positioned in a triangle formed by the railroad trestle and bridge over John Nolen Drive.

The 16-foot-wide, solar-powered machines -- which suck water from the bottom of the lake up through a tube and distribute it on the surface over an area of up to 50 acres -- were designed to attack blue-green algae by circulating water and disrupting the habitat.

Some residents around the bay were optimistic the SolarBees could help eliminate smelly, and sometimes toxic, blue-green algae blooms, as well as reduce weeds and improve water clarity.

But the state Department of Natural Resources and UW-Madison faculty warned they could actually create algae blooms by stirring up nutrients in the water.

Jeff Swiggum, a member of Friends of Monona Bay who lives off of the bay on Lakeside Street and walks by it each day on his way to work, said he was "rather ambivalent" about the SolarBees.

"There was no real good data prior to their placement," Swiggum said. "There were a lot of weeds out there this year. Could there have been more had we not had SolarBees? We don't know."

Swiggum said he's not upset to see them go.

"There may be some people who look at the SolarBees as finally, the city is doing something. It may be more symbolic. ... On the other hand, there were a lot of people who felt they were a big waste of money," he said, adding that some residents saw the devices as "big ugly thing collecting bird feces."

"Maybe having weeds in the bay is not such a bad idea," Swiggum said. "Without weeds, it can just become an algal cesspool."