Greymouth whitebaiters were unpleasantly surprised by the sight of raw sewage drifting past their nets in the Grey River.
The die-hard fishermen apparently have recent heavy rain to blame for the pollution.
Grey District Council assets and engineering manager Mel Sutherland said the current sewerage system, which combined stormwater and wastewater, simply could not cope in the rainy season, creating overflow which was diverted to the river.
The problem was a hangover from the days when all of Greymouth's raw sewage flowed freely into the river, and it should be rectified by next June.
The original systems for Greymouth, Cobden and Blaketown combined wastewater and stormwater, which was discharged to creeks and the Grey River.