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 Council said 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.
