ST. PAUL, Minn. (AP) — The Minnesota Pollution Control Agency has opened a 30-day public comment period on proposed changes to the state's water quality standards for protecting wild rice.

State law currently limits discharges of sulfates into wild rice waters to 10 milligrams per liter. The MPCA has proposed changing that to a site-specific approach based on the characteristics of individual water bodies. The draft proposal also would establish criteria for determining which lakes and streams will be designated wild rice waters, and includes initial lists.

It's been a contentious issue, pitting mining interests against American Indian tribes and environmentalists.

The MPCA is taking comments through Dec. 18. It will consider those comments as it develops formal rules.

The agency says it intends to adopt rules by 2018 but hasn't formulated a schedule.

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