NICOLVILLE, MINN. -- Flush a toilet in this community of 16 houses, and the raw sewage flows into Dobbins Creek.

Flush a toilet in an estimated 64,000 other homes across Minnesota, and the same thing happens: Untreated waste illegally ends up in creeks and ditches or bubbles above ground from failed septic systems.

The sewage is an "imminent threat to public health and safety" under state law because it spreads disease-causing bacteria. At least 95 Minnesota rivers have excessive fecal contamination, much of it from untreated waste.

State or local regulators have known about violations for years. But inconsistent and lax enforcement of regulations is allowing unsanitary conditions to persist. It's a problem across farm country, where illegal sewers have existed for decades.

"It's hard to believe that in Minnesota, the land of sky-blue waters, we still have communities like that, but there are a lot more than people think," said Jeff Freeman, assistant director of the Minnesota Public Facilities Authority, which helps finance wastewater treatment projects.

Towns that can't afford to fix the problem keep polluting. Here in Nicolville, 6 miles east of Austin, homeowners are facing potential bills of $22,000 each to construct a community treatment system. Some residents are elderly and living on fixed incomes. Regulators say they will not take legal action as long as residents work on a way to solve the problem.

But no fix is in sight in many communities. For Susan Hodge, it's already too late. She recently lost her Nicolville home to the bank. "I couldn't afford to stay here," she said.

Below Nicolville's sewage outlet pipe on Dobbins Creek, fecal bacteria have been measured at 11 times the level allowed in surface water. It flows into East Side Lake, which is part of a city park in Austin.

The bacteria thrive in human and animal intestines and are transmitted to water from untreated sewage and feedlot runoff. Drinking or accidentally ingesting tainted water can cause diarrhea, nausea and possibly jaundice. Swimmers, divers, water skiers and windsurfers are most at risk.

Children wading in such waters are at risk because they are likely to put their hands in their mouths or to fall in. Those who get sick may never know the source; epidemiologists say waterborne disease can be hard to track.

'That's what rivers are for'

When Sara Christopherson was growing up in the 1980s on a farm near Cologne, in Carver County, the family's sewer line connected to a drainage pipe that went to a ditch.

Since then, she said, "I can't tell you how many property owners I have talked to who do not think it is a problem."

Her family's system eventually got fixed, and Christopherson went to work for the University of Minnesota Water Resources Center. She now teaches extension courses for septic industry officials.

Across the state, she and other officials said, many homeowners connected septic tanks decades ago to cropland drainage systems known as drain tiles.

"I've heard it referred to as the farm system," Christopherson said. The pipes send untreated waste into ditches and streams.

People still think "that's what rivers are for -- to get rid of stuff," said Bea Hoffmann, executive director of the Southeast Minnesota Water Resources Board, which does research, training and outreach. She said that thinking needs to change: "Why in 2006 do we have raw sewage going into streams? It sounds like something you would expect in the developing world."

In Hope, Minn., a town of 120 people south of Owatonna, sewers from most of the 52 homes connect to a pipe running into the Straight River. The pipe was laid in the 1930s for storm water, but people connected septic tanks to it.