Stretches of area rivers are polluted with a popular corn pesticide, according to the Minnesota Pollution Control Agency.

The agency is recommending the rivers be designated as impaired — the first time the state has recommended that designation because of pesticide contamination.

The result could be requirements on farmers to significantly reduce the amount of the pesticide entering the rivers.

Marvin Hora, manager of the water assessment section at the MPCA, said the pesticide — cetochlor — is one of a new breed of pesticides and the first to show up in the rivers.

“There were some old-line pesticides like DDT that have shown up in the water before, but this is the first time a modern pesticide has been detected and listed,” Hora said.

The MPCA said portions of the Blue Earth and Le Sueur rivers, a ditch that empties into the Cobb River, a river in Carver County and the middle branch of the Whitewater River in southeastern Minnesota contain acetochlor, used to control weeds in corn crops. The chemical has been measured in the rivers at various times between 1998 and 2005 at concentrations up to five times higher than the state limit for what’s considered environmentally sound.

While only short stretches of each river are listed by the state — because that’s where their monitoring equipment is — it’s likely the pesticide will be found elsewhere in the rivers when further studies are done.

“We don’t want the pesticide that’s applied in the field to end up killing the aquatic plants in the stream that are essential for the health of that stream,” said Dave Christopherson, water quality research analyst for the MPCA.

The issue highlights the potential conflict of cultivating a growing corn crop in the same watershed that the public expects to be pristine.

Sold under the brand names of Harness and Surpass, acetochlor is usually applied in late spring, near planting time, but before corn plants have emerged. Farmers say it controls weeds and boosts yields — important as the demand for corn increases with the demand for ethanol.

Hora said the rivers will be placed on the proposed list of impaired waters this fall and the final list will be sent to the federal Environmental Protection Agency next spring.

Once listed as impaired, a more detailed study will be done of the rivers to measure levels of the pesticide and the source of the pesticide. That’s a process that could take years.

Once the source of the pesticides is found, the EPA requires the state to take actions to bring the rivers back into compliance.

“Whatever it takes to prevent the acetochlor from entering the river and get the water back within standards,” Hora said.

Farmers have halved their use of the chemical in recent years, said Steve Sodeman, a crop consultant in the St. James area of south-central Minnesota. Sodeman, who also serves on the board of the Minnesota Corn Growers Association, said just because scientists can measure chemicals does not mean extremely low concentrations are risky.