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An unrelenting late summer deluge swamped parts of western and central Wisconsin on Monday and Tuesday leading to emergency declarations in six counties.

Already waterlogged Madison was mostly spared from the worst storms Tuesday, but city officials continued to urge caution about flooding risks. They also warned about a related danger: Last week’s storm swept hundreds of thousands of gallons of untreated wastewater into the local lakes contributing to an increase in hazardous bacteria levels.

Gov. Scott Walker declared a state of emergency for Fond du Lac, Juneau, La Crosse, Monroe, Vernon and Washington counties, adding to the emergency declared for Dane County last week.

Dane County on Tuesday was projecting the already flood-bloated Yahara River lakes could rise another 2 inches as intense thunderstorms were forecast to sweep across southern Wisconsin.

Two of the lakes — Monona and Waubesa — exceeded their highest recorded levels after the Aug. 20 storm. Lake Monona had begun to drop Sunday and Monday. County crews cut aquatic weeds downstream in the Yahara to allow water to flow more freely.

It was likely that floodgates in the Tenney dam would be opened wider to allow water to flow more quickly out of Lake Mendota, through the Yahara River channel across the Isthmus and into Lake Monona, Mayor Paul Soglin said Tuesday.

Preventing Lake Mendota from rising too much protects against a possible catastrophic breach in the dam, which holds the lake about five feet higher than its natural level.

But releasing water more quickly into the Yahara River channel backs up storm sewers, causing Isthmus streets to flood. It also sends more water into flooded areas around Lake Monona and other downstream lakes.

More thunderstorms were possible through the weekend, the National Weather Service said.

“Flooding impacts will be closely tied to where the heaviest rainfall occurs,” the weather service said. “The risk for flooding will be highest where heavy rain has already fallen over the last week or so.”

Fresh round of floods

Between 5 and 11 inches of rain fell over the western counties of La Crosse, Vernon and Monroe overnight Monday, causing evacuations in some communities due to flash flooding.

In Coon Valley, a town of about 765 people just southeast of La Crosse, emergency responders helped residents evacuate Monday night and into Tuesday morning. People also were evacuated in the villages of La Farge and Readstown on Tuesday.

Tens of thousands of customers were without power Tuesday night from more storms that moved across central Wisconsin throughout the afternoon and evening, according to Alliant Energy and We Energies, largely concentrated near Fond du Lac.

The National Weather Service also reported possible tornado damage in a swath extending from southern Marquette County across Green Lake County and into Fond du Lac County.

Unpredictable floodwaters

As Dane County girded for expected rising lake levels and more flooding of Isthmus streets, authorities urged caution for anyone tempted to wade or boat in floodwaters.

Increased levels of hazardous bacteria were detected in water after the record Aug. 20 deluge that washed hundreds of thousands of gallons of untreated wastewater into the Yahara River lakes.

Since then, pathogen concentrations have dropped, but swimming areas remain closed because sampling has been limited and conditions can change rapidly, Public Health Madison and Dane County spokeswoman Sarah Mattes said Tuesday.

“All beaches are closed due to high water levels, an increased risk of waterborne illness, and increases in debris from flooding,” Mattes said.

Madison Metropolitan Sewerage District said the record-breaking rainfall from the Aug. 20 storm that started the flooding overwhelmed sewer pipes in four locations and caused an estimated 676,000 gallons of untreated wastewater to be released.

Some sewage from the spills reached Lake Wingra, which drains into Lake Monona; and Middleton’s Esser Pond, which empties into Pheasant Branch Creek on its way to Lake Mendota. A small amount reached Dunn’s Marsh on Madison’s West Side.

Heavy rainfall quickly saturates soil and then runs across its surface picking up contaminants and debris. Runoff also scours ditches, roads and polluted industrial sites flushing harmful substances into streams and lakes.

Flooding often carries sewage, animal wastes, petroleum products, fertilizers, and other contaminants into lakes and streams, Mattes said.

“Beaches will reopen once they no longer pose a risk to health and safety,” Mattes said.

Safety concerns

Soglin highlighted the hazards of coming in contact with floodwaters, whether in the lakes or the streets.

“It might be nice to have a selfie canoeing or kayaking on a city street, (but) it’s not safe,” Soglin said.

Unpredictable currents can capsize a canoe and dump paddlers into contaminated waters, Soglin said.

People who walk barefoot in the water face injury if they step on sharp, submerged debris or broken pavement, the state Department of Natural Resources said.

Heavy rains and flash floods across southern Wisconsin have damaged roads and created sinkholes, said April Dombrowski, head of the DNR Bureau of Law Enforcement’s Recreation Safety and Outdoor Skills Section.

When boating in abnormally high waters, it’s especially important to check on local water conditions, maintain safe speeds and wear a life jacket, Dombrowski said.

“What may look like a simple branch floating downstream may be the top of a large tree or branch below,” Dombrowski said. “Sunken docks and other items may be hidden from view.”

High water erodes shorelines, and the problem is worsened by boat wakes, she said.

No-wake restrictions continued to be in effect on Lakes Mendota, Monona, Waubesa and Kegonsa.

Shoring up

In Madison on Tuesday crews were reinforcing eroded Lake Monona shoreline with rocks. One inbound lane of John Nolen Drive was to be closed between 9 a.m. and 3 p.m. through Friday to make room for equipment.

“Crews will work to maintain a portion of the bike path for pedestrians and bikes, but bicyclists are asked to walk their bikes,” city officials said.

East Washington Avenue on Tuesday had all lanes open in both directions, which took some pressure off the other streets in the Isthmus. But streets were likely to be closed again if the Tenney dam flow is increased to prevent Lake Mendota from breaching the dam.

The latest street closings can be found on the city’s flooding page at www.cityofmadison.com/flooding.

Highways, bridges damaged

Several Dane County highways were still closed by floodwaters or damage.

  • Highway KP from Black Earth west to Highway F had one lane closed.
  • Highway W from Highway B to East Church Road near Utica.
  • Highway J from Old Military Road to Highway S.
  • Highway G from Highway J to Marsh View Road.

One bridge was damaged and another washed out on Highway 14 in Black Earth, and the Wisconsin Department of Transportation is recommending replacement of both spans. Traffic is detoured to Highway 12 and Highway 78 to get around the Black Earth damage.


The Associated Press contributed to this report.


[Editor's note: This story has been updated to reflect two corrections.

The original incorrectly described the reasons officials advised against contact with floodwaters. Public Health Madison and Dane County has detected high bacteria levels near beaches, but testing of water samples taken in response to the release of 676,000 gallons of untreated wastewater at four locations by the Madison Metropolitan Sewerage District hasn’t been completed.

One stretch of closed highways was also incorrect. The affected road is Highway G from Highway J to Marsh View Road.]

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Steven Verburg is a reporter for the Wisconsin State Journal covering state politics with a focus on science and the environment as well as military and veterans issues.