About 15,000 cubic metres of raw sewage has flowed into an area of mudflats at Nelson after a sewer main leak this morning.
The public are advised not to swim, be in contact with water, or collect shellfish at the Nelson Haven tidal inlet until further notice.
Nelson City Councilsaid a large leak on the sewer main near Corder Park pump station was discovered at 7.20am.
It resulted in 12,000 to 15,000 cu m of untreated sewage being discharged. Repair work was underway and expected to continue all day, the council said.
Warning signs were put up and the swimming ban was expected to remain in force until several tidal flushes had cleared the sewage.
The council will notify the public when it is safe to swim again.
Nelson Marlborough District Health Board Public Health Service, Ministry of Fisheries, Department of Conservation, pollution control officials and local iwi have been notified.
Nelson Haven is a tidal inlet separated from Tasman Bay by a breakwater, and an important habitat for wading birds.
