ST. PAUL, Minn. — Gov. Mark Dayton has warned lawmakers he'll veto a bill to nullify the state's wild rice water quality standard if it reaches his desk without changes.

The governor said in a letter Thursday he recognizes it's not technically or economically feasible for the mining industry or municipalities to comply with the existing standard, which limits discharges of sulfates into waters where wild rice grows to 10 milligrams per liter.

But he says the bill as written is an "extreme approach that removes important protections for wild rice, conflicts with federal law and guarantees ongoing litigation."

The bill has cleared a conference committee and is headed back to the House and Senate for final votes. It's supported by mining backers and wastewater plant operators, but opposed by tribal and environmental groups.