Environmental groups pushing the federal government to take over enforcement of Clean Water Act regulations in Iowa said Tuesday that Gov. Terry Branstad is lobbying on behalf of agriculture groups, ignoring the environmental damage being done to rivers and streams by manure spills and farm runoff.

Iowa Citizens for Community Improvement, the Environmental Integrity Project and the Iowa Sierra Club filed a Freedom of Information Act request seeking documents about negotiations between the U.S. Environmental Protection Agency and the Iowa Department of Natural Resources.

The documents, obtained by The Associated Press, show that Branstad and Lt. Gov. Kim Reynolds wrote to top EPA officials in Washington on May 20, bypassing the regional EPA office in Kansas City that had been directly involved in the negotiations with Iowa’s natural resources officials.

The letter was written to Acting Administrator Bob Perciasepe and Gina McCarthy, President Barack Obama’s nominee to become EPA administrator. In it, Branstad and Reynolds express “strong concern” with an EPA proposal to investigate livestock farms with more than 750 animals.

“Our philosophy is to proactively work with farmers as partners, who are under the state’s regulatory jurisdiction, to ensure an understanding of the rules, regulations and best practices to prevent negative impacts on our natural resources, instead of using the “gotcha” approach in initiating investigations broadly,” the letter said.

Iowa Citizens for Community Improvement spokesman David Goodner said Branstad is trying to tip the scales by putting pressure on the EPA to back off.

“It’s important that Iowans understand exactly what the governor is doing, that he is personally involved and that he is weighing in on behalf of the industry without a shred of concern for water quality and the burden that imposes on everyday Iowans,” he said.

“This letter shows the governor’s office is out of touch with the water quality reality in Iowa,” said Tarah Heinzen, attorney for Environmental Integrity Project. “We’re seeing record levels of pollution.”

Iowa, the nation’s leading pork producer, had 20.1 million hogs on farms in June. Most are raised inside large hog confinement buildings and controlling the manure has become a sore spot for environmental groups.

Since 1995 the state has had about 800 manure spills. The state also has seen its number of polluted lakes, rivers and streams increase. The EPA listed more than 600 impaired waters in Iowa in 2012 up from 594 in 2010.

Branstad spokeman Tim Albrecht said Branstad and Reynolds “are working hard to protect our waterways, while standing up for all Iowans...” He said they want to ensure that any changes to the regulations of do not go beyond the scope of EPA’s authority “and do not become overly burdensome to Iowa’s farm families or our communities.”

Branstad and DNR officials have come under increasing criticism this spring as runoff of fertilizer and manure from farms has boosted the level of nitrate in rivers and streams.

Des Moines Water Works, which serves 500,000 residents in central Iowa, has struggled to keep its water below the EPA safe level of 10 milligrams per liter by using a nitrate removal system that costs $7,000 a day to operate.

General Manager Bill Stowe has said if the water goes over the EPA safe limit and Iowa policymakers fail to sign off on a plan to regulate farm runoff, Des Moines Water Works may file a lawsuit asking a federal court to force the EPA to establish standards limiting runoff and enforcement.

The environmental groups also are prepared to sue the EPA for unreasonable delay if the agency doesn’t push the state harder to begin cleaning up livestock operations.