MINNEAPOLIS  — Gov. Mark Dayton said Friday he has reluctantly told environmental officials to back off private ditches as they prepare to start enforcing his marquee water quality initiative — stronger requirements for leaving buffer strips of vegetation between farm fields and waterways.

Passing the requirements was a major flashpoint at the Capitol last year, and it continued over concern about implementing the buffers along private ditches. Top Republican lawmakers and agricultural groups have said the compromise law was never intended to cover private ditches on a large scale, something House Speaker Kurt Daudt reiterated on Friday.

The governor told the Department of Natural Resources not to include those ditches when mapping where the law will be enforced. He also said in a statement that GOP leaders had threatened not to consider borrowing requests for water quality improvements from the DNR and the Board of Water and Soil Resources in the upcoming session if private ditches weren’t exempted, calling it “fierce opposition by the House Republican leadership.”

Later Friday, he stressed at a news conference that private ditches eventually flow into public waterways.

“(If) that water that’s in those ditches is not being cleaned up, it’s going to totally sabotage the effectiveness of the legislation, which is to protect the people of Minnesota,” he said.

Daudt denied that Republicans threatened to withhold funding sought for water quality projects.

Officials aren’t how sure much farmland might be affected by Friday’s decision. The administration had said its buffer initiative would establish 110,000 acres of grass and other plant cover to protect state waters from polluted runoff. The law requires buffers averaging 50 feet along public waters and a minimum of 16.5 feet along public ditches; widths on other waters will be determined by local soil and water conservation districts.

John Jaschke, BWSR’s executive director, said private ditches have never been mapped, but guessed that Friday’s decision will exclude a relatively “small portion” of them. He also pointed out that the law still allows local governments to identify private ditches that could use buffers and put them in place through voluntary measures or local requirements.

Two key committee chairmen on environmental issues, Rep. Denny McNamara, R-Hastings, and Sen. David Tomassoni, DFL-Chisholm, wrote to the DNR commissioner in November to say that the agency was misinterpreting the law by asking local governments for data on private ditches. Including anything but public ditches went “far beyond” what the House and Senate negotiated with the administration, they said.

The scale-back will ultimately weaken the new law’s efficacy in reducing water pollution from farm runoff, said Sen. John Marty, a Roseville Democrat and longtime supporter of efforts to boost water quality. He dismissed the idea that farmers should be able to do as they wish with their private ditches, most of which would ultimately feed into groundwater sources or public drainage systems.

“The trouble is, they don’t live on an island. They are polluting their neighbor’s water,” Marty said. “I don’t think farmers want to live in the land of 10,000 cesspools.”

But Minnesota Farm Bureau lobbyist Doug Busselman said the state agencies were going beyond the intention of the law. He said it was appropriate to include public ditches in the law because they’ve been legally defined — “as opposed to someone arbitrarily saying, ‘That’s a ditch.”’ He argued that farmers were never given a clear indication of what other private lands would be affected.

He argued that farmers were never given a clear indication of what other private lands would be affected.