It's the best time of year to hit Minnesota's lakes -- it's hot outside and most of the water is at a comfortable temperature to swim. But you're likely to encounter a thing or two that might make you squirm.
Eurasian watermilfoil, an invasive weed, has infested most lakes in the Twin Cities area. Many lakes and rivers in greater Minnesota also have the weed. Nothing happens if you touch it, but it can be unpleasant to swim in. If it gets too thick, swimmers have been known to get tangled in it, which is a hazard. Milfoil is also a problem for boaters -- if the weeds are thick on the surface, boats can get stuck.
If the water in the lake you're visiting is green, algae has likely taken over. It's caused by excessive nutrients in the lake, mostly from storm water runoff. Everything from leaves to grass clippings to fertilizers can end up in the lake, causing algae blooms. Algae makes the water less clear, but it can also become a hazard if the conditions are right.
Blue-green algae, found mostly when it's extra warm outside, can contain toxins that may be fatal to dogs and other animals if they ingest it. It can also cause skin irritation and upper respiratory problems for both animals and humans.
"It's a fairly good year for algae conditions in the state," said Matt Lindon of the Minnesota Pollution Control Agency.
A wet spring led to extra runoff in the lakes, which means more nutrients for algae to feed on.
While blue-green algae tends to show up later in the summer, it's already been found on a few Minnesota lakes. That includes a neighborhood lake in Little Canada called Round Lake, where officials said low water levels and stagnant conditions might have contributed to the problem.
Cliff Aichinger, administrator of the Ramsey-Washington Metro Watershed, said signs are up to warn people. But he said it's not a lake that's used for swimming or boating, and so far the toxin levels are low.
"It can get really nasty," he said of blue-green algae. "This is not that bad."
E. COLI and COLIFORM BACTERIA
Every summer, local health departments test swimming lakes for E. Coli or fecal coliform bacteria. If there's enough of it in the water, officials will post advisories or sometimes even close beaches. Minnesota Department of Health officials said so far this year there haven't been problems with bacteria. But it will likely pop up later this summer.
Swimmer's itch is caused by a type of worm that gets into the skin and causes red, itchy welts. The organism starts in the intestinal tracts of ducks and other water birds, so officials recommend refraining from feeding ducks and trying to keep them away from swimming areas. Swimmer's itch is another annoyance that's more common later in the summer.