PARK RAPIDS — Park Rapids residents will see their water bills go up about 25 percent to help pay for a water-treatment plant, but some residents are angry that they’re paying to clean contamination caused mostly by farmers.

The city’s water supply has become contaminated with nitrates from agricultural fertilizer. The city will be bringing its $2.5 million treatment plant on line next month, which could cost local families about $130 more in annual water bills.

Dick Rutherford, who owns two homes in town, said he doesn’t think he should be paying for someone else’s carelessness.

“We know where it’s coming from,” he said. “It’s the farmers that are putting this stuff in the ground. I don’t feel we should be paying for the whole thing, I don’t think we should be paying for any of it.”

Park Rapids is in north-central Minnesota and has a population of 3,700. Agriculture is big business there, but now an aquifer that used to provide plenty of clean drinking water has nitrate concentrations two to three times higher than safe levels, according to the state Department of Agriculture.

The state has already begun working with local farmers to reduce water and fertilizer use. About 50 farmers took part in a monitoring and education program last year, said Luke Stuewe, who coordinates the program for the agriculture department.

“Sixty-five percent of the growers involved in the program found they could make adjustments to their rate and the majority of those were reductions in rate,” Stuewe said.

Some farmers have turned to a slow-release fertilizer that reduces leakage to groundwater. Others are planting crops that need less nitrogen.

Even with the changes, however, nitrate levels in wells are still going up. Some of the aquifers are 70 feet below ground or deeper, so it could take years for changes above ground to improve water quality.

Research suggests that elevated nitrates in drinking water can endanger young infants. The risks to older children and healthy adults are still being studied.