A pump station overflow north of Auckland has resulted in the temporary closure of Oyster farms and the destruction of thousands of contaminated oysters.

In an email sent on Thursday, Watercare said the pump station overflowed at about 2.30pm to the stormwater pond and wastewater began entering the Mahurangi River but the overflow was not stopped until 8am the next day.

Chair of the Mahurangi Oyster Farms Association, Lynette Dunn, said to Andrew Dickens that this was far from the first time this type of incident had occurred.

"I think by recording, we might be up to about 38 or 39 times for the whole year," she said. 

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