MEDFORD, Ore. (AP) — Water quality advocates filed a lawsuit alleging the city of Medford has known for years that water discharged from its sewage treatment plant illegally harms the Rogue River's aquatic balance but failed to fix it.

The Northwest Environmental Advocates, in a suit filed Tuesday, claim studies since 2013 show nutrient levels cause unnatural algae and aquatic weed growth, damage underwater insects and at times create a sudsy, smelly plume on the river, the Mail Tribune reported .

One of the studies was funded by the city, according to the lawsuit.

The suit seeks to force the city to stop violating the Clean Water Act and start removing more nitrogen and phosphorus from treated water before it's discharged.

"They need to remove the nutrient pollution that everybody believes is the source of the pollution," Northwest Environmental Advocates Executive Director Nina Bell said.

Bell said Medford's "sit-on-your-hands approach" to dealing with the plant's discharge problems has been "a disservice to its rate-payers and the environment."

Medford Public Works Director Cory Crebbin said he was unaware the suit was filed and could not comment on it.

"As far as I knew, we were still in negotiations," Crebbin said.

The advocates also scolded the state Department of Environmental Quality for "essentially protecting Medford" by not holding the city accountable for discharge pollutants since they were documented by the studies.

The Department of Environmental Quality is not a party to the lawsuit and is not in a position to comment on it, agency spokeswoman Katherine Benenati told the Mail Tribune in an email.

The lawsuit seeks civil penalties of more than $52,000 a day for violations.

The suit does not ask Medford to stop discharging water while the case plays out in court.

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Information from: Mail Tribune, http://www.mailtribune.com/