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.
Stage one of the new treatment plants for Greymouth and Cobden have been designed and consented to treat the combined wastewater and stormwater flows, but only up to a certain volume.
Mr Sutherland said they had achieved a significant environmental improvement but they were not designed to cope with all the flow in wet weather.
The council is currently separating the stormwater and wastewater pipes so that a new treatment plant can be built to treat only the wastewater flows.
A West Coast Regional Council consent hearing is taking place this week for the proposed stage two treatment plant in Preston Road.
When it is operational, all properties in Blaketown, Boddytown, Cobden and Greymouth will be connected to the new separated wastewater pipes in the street.
"Barring disruptions to service there should no longer be any untreated effluent being discharged to the Grey River," Mr Sutherland said.
- The Greymouth Star