Three public beaches in the western Lake Minnetonka community of Mound were closed Monday after heavy weekend rains forced about 20 Minnesota cities and industries to bypass their sewage treatment operations and channel untreated waste into lakes and streams.

The impact was felt from the Iowa border to the Iron Range, said Wendy Turri, municipal wastewater manager for the Minnesota Pollution Control Agency. Most cities that used the bypasses were able to discharge sewage into rivers or other bodies of water not used for recreation, she said. But in Mound, an overwhelmed sanitary sewer system forced the discharge of contaminated wastewater into heavily used Lake Minnetonka.

In the coming days, contaminated runoff from streets — not from sewer pipes — could lead to other restrictions, said Duane Hudson, environmental health program coordinator for Hennepin County. Monday’s beach closures were the result of “an abundance of caution,” because the results of lakewater tests are not yet in, Hudson said.

The treatment-plant bypasses came when the amount of rain caused so much seepage into sanitary sewer pipes that they became clogged, creating the potential for sewage backup into homes. Nearly 1,000 homes in Mound were facing that possibility when the city notified the MPCA it was bypassing its sewage treatment plant Sunday. It returned to regular treatment operations early Monday, but about 20 homes were contaminated and will be uninhabitable until they’re cleaned up, said Mound city manager Kandis Hanson.

It’s not uncommon for Minnesota beaches to be closed due to E. coli contamination, since it can also be produced by waste from geese, ducks and other wild animals, as well as from boaters dumping waste overboard.

Hanson said that although the sewage discharged Sunday was clear and contained no visible solids, it was nearly certain to have contaminated water. “It should dissipate quickly — the same as goose poop,” she said.

An infrastructure question?

Mound Mayor Mark Hanus said he doesn’t remember the city ever having to pump sewage into the lake. He blamed the problem on what he called outdated regional sewage mains overseen by the Metropolitan Council that service the west side of Lake Minnetonka.

State Sen. David Osmek, R-Mound, said the Met Council has promised a major upgrade for about a decade but hasn’t delivered. In the meantime, he said, Mound has put hundreds of thousands of dollars into fixing city mains.

Sewer upgrades are in the works around the region, but “past and future planned improvements would not have prevented this spill because it resulted from extremely excessive amounts of rainwater,” Met Council spokeswoman Meredith Vadis said in an e-mail. “We are working with Mound and some four dozen cities in the metro area to prevent this excessive flow of clean water from getting into local and regional sanitary sewers in the first place. That is a much more targeted and far less costly alternative, as compared to vastly increasing sanitary sewer capacities to take on stormwater that enters the sanitary sewers from occasional but extreme rainfalls.”

On one Lake Minnetonka beach, at least some residents were taking things in stride Monday. Sarah Hinck and Miriam Swanson had the beach at Surfside Park to themselves.

Hinck, 29, of Mound, said she’s been going to Lake Minnetonka her whole life. This time of year, she said, it’s common for swimming to be prohibited — though she doesn’t remember a warning quite like this one.

“If it’s during this time of year, no one really gets in the water anyway,” Hinck said.

High lake, high creek

Meanwhile, Lake Minnetonka rose Monday to its highest level on record. The jagged-edged, 14,000-acre lake was a foot higher than it was at the end of April, 5 inches higher than it was Friday and 1.5 inches higher than the previous high-water record set in September 2001.

Many shoreline docks were covered with water, said Minnehaha Creek Watershed District spokeswoman Telly Mamayek. No-wake restrictions remained in place on the lake, and the MCWD renewed warnings to canoeists and kayakers to stay off the creek.

Storm cleanup elsewhere in the metro area continued Monday. The city of Eden Prairie condemned a home that was undermined by a back yard mudslide Sunday. And in Edina, officials reopened a street that had been closed due to high water but were advising residents who sandbagged their properties along Minnehaha Creek to keep the protection in place.

The forecast suggests that more thunderstorms might be possible Thursday and Friday in the Twin Cities. The national Climate Prediction Center had identified strong chances for a wetter-than-normal June across much of Minnesota, with cooler-than-normal temperatures.

The up side of rain

The weekend rains made this the second-wettest January-through-June 1 period on record in the Twin Cities, with 16.84 inches of precipitation at Minneapolis-St. Paul International Airport. Normal for the first five months of the year is about 9.58 inches. The record of 19.47 was set in 1965, a year of disastrous spring flooding.

These rains may actually have been well-timed. With emerging leaves and other new plants happily lapping up moisture, much of what might have run quickly into rivers in late summer, fall or early spring is instead being used up by greenery, said Craig Schmidt, hydrologist with the National Weather Service office in Chanhassen. As of Monday, no disruptive flooding was expected along any rivers across southern Minnesota and west-central Wisconsin through the rest of the week.

Flood watches across most of the state steadily evaporated Monday, even in northeastern Minnesota, where the heavy rain moved after leaving central and southern Minnesota. Hibbing received more than 6 inches between Saturday morning and midafternoon Monday.