High levels of norovirus are polluting Whangarei harbour following an outbreak of gastroenteritis in resthomes in the North Island city.
Northland Health has closed the harbour for shellfish gathering for two months after tests revealed the virus in the city's wastewater and upper harbour.
It says norovirus finds its way into sewage during community-wide outbreaks and a rain storm earlier in May caused sewage spills in the harbour.
Six resthomes in Northland have reported widespread illness caused by norovirus and it has been linked to the deaths of two elderly residents.
Northland Health says five of the six resthomes now have the highly infectious bug under control - but it has also been rife in the general community.
Harbour pollution after storms usually results in a one-month closure for shellfish gathering.
But Northland Health says it is advising a two-month closure this time due to the high rates of infection.