Oh, joy: a big year for milfoil

There's more: milfoil-munching weevils won't work in Southwest lakes

If you've been walking, biking or driving around the lakes lately you've seen the large pockets of dark brown weeds floating on the surface -- the telltale presence of milfoil. Lakes stay clear during cool, dry weather, but the milfoil growth has exploded with the last three hot and humid weeks.

Jeff Lee, the Environmental Operations Manager for the Minneapolis Park Board, said he can't call this a record year for milfoil because no official statistics are kept. However, he said the milfoil presence was much more “robust” than he’s seen in the last several years.

"There are two harvesters working six to 10 hours a day cleaning out milfoil," he said.

The harvesting machines work like a big lawn mower, cutting off the top four inches of weeds. About 20 tons of milfoil are collected daily and taken to a composter.

The harvesters have cut milfoil at Lake Calhoun and Lake of the Isles for about three weeks, focusing on primary recreation areas such as beaches, docks and the channel between Calhoun and Isles. The harvesters plan to finish cleaning Lake Harriet and move on to Cedar Lake after the July 4th weekend.

Too many fish

Lee said that the Park Board recently learned that milfoil-munching weevils are being gobbled up by Southwest lakes' huge pan fish population.

Bluegills, walleyes and muskies are eating the weevils faster than the weevils can consume the milfoil. "You need a critical mass of weevils to have an impact on the milfoil - and they don't have enough time to generate that," says Lee.

There's not much chance that more fishing will help, since city lakes have 10 times the fishing use as the average Minnesota lake. Also, during prime conditions, milfoil grows about an inch a day, Lee said.

He added that milfoil is a healthy part of the lake eco system. "You have to keep in mind that even if we were able to get rid of all the milfoil, we aren't allowed to do that," he said. "We have to keep about 50 percent. Just because there are weeds in the lake, doesn't mean the water quality is poor."