Sewage leaked into the River Erewash on Tuesday after a power cut at a Langley Mill treatment plant.
Environment Agency staff worked through the night after the leak at Milnhay Sewage Treatment off Brookvale Road.
“We have been notified by Severn Trent Water that a powercut at Milnhay Sewage Treatment Works has led to some partially treated sewage getting into the River Erewash in Derbyshire,” said an agency spokesman on Tuesday night.
“There has been a slight dip in oxygen levels, but we’ve not seen any fish in distress at this stage.”
Workers, who added peroxide to the river, reported oxygen levels were back to normal on Wednesday morning.