GREAT FALLS (AP) — People who live downstream from a proposed coal-fired power plant east of here plan a meeting later this month to discuss concerns about mercury emissions and the amount of water the 250-megawatt plant would use.

‘‘There are a lot of us who are concerned about this plant,’’ said Lisa Hardiman, a member of the Missouri River Citizens group.

Hardiman said she also planned to invite Anne Hedges, program director with the Helena-based Montana Environmental Information Center, to attend the April 19 meeting.

The Southern Montana Electric Generation and Transmission Cooperative argues the $515 million plant will be the cleanest coal-fired power plant in the state, with a draft air quality permit that requires removal of 90 percent of mercury from the emissions.

Chouteau County Commission Chairman Jim O’Hara said he isn’t opposed to the coal burning technology, but worries about the amount of water the plant will pull from the Missouri River.

‘‘Irrigators are important to Chouteau County,’’ he said. ‘‘A few years ago the river was so low we almost cut off irrigators. We need to know more in case we get another dry year, and they are using a lot more water upstream.’’

The city of Great Falls plans to sell Southern Montana Electric 4.6 million gallons of water per day from its Missouri River reservation of 5.8 million gallons per day. The city has total water rights of 75.1 million gallons per day from several sources.

Experts say the water sale would not jeopardize the city’s water supply and would not create a new water right for the plant.

The Department of Natural Resources and Conservation is reviewing the water rights change. The public will receive notice when a draft environmental impact statement for the plant is released.

Elsie Tuss, who has an organic ranch downwind from the proposed plant, worries mercury could contaminate gardens and grass.

‘‘How do you sell organic cattle fed by mercury-laden grass?’’ Tuss asked.

Jeff Chaffee, vice president of Bison Engineering in Helena, the environmental engineering consultant for the proposed plant, said organic crop guidelines are primarily based on pesticide controls.

‘‘This plant will be very well controlled and subjected to stringent emission limits designed to protect downwind public health, the environment and entities, including crops,’’ Chaffee said.