The clean-up of a polluted waterway in Lincolnshire is due to be completed next week.
The Environment Agency said sewage had been leaking unnoticed into the water at Chain Bridge near Boston for the past 10 years.
About a mile of the drain had been affected by the leak, which was traced back to a crack in a sewer pipe at a nearby firm.
The final clean-up of the waterway is due to take place on Tuesday.
But it could take until next summer for water quality to recover, experts said.