A study commissioned by fly-fishing groups contends the effluent released from Medford's wastewater treatment plant illegally harms insect life and promotes unwanted algae growth in the Rogue River.
The study says the pollution could harm chinook salmon eggs laid in gravel downstream of the treatment plant near TouVelle State Park.
One of the study's sponsors says state and local officials should set a schedule for investigating and fixing the problem.
The Medford Mail Tribune says city officials are calling the study's conclusion premature.
The city says the plant's releases are always within state water-quality standards, and the study shouldn't blame the plant for impacts on plant and animal life without taking into account other possible factors.