Health officials are warning people in Christchurch to avoid contact with all rivers, seawater and ponds because of the renewed risk of a gastroenteritis outbreak.
The Canterbury District Health Board is stressing that all drinking water should be boiled, regardless of where people live in the city.
The board says the latest earthquakes have caused more damage to pipes, and more untreated human sewage is being discharged into waterways.
It says testing at some beaches between the Waimakariri river and Lyttelton harbour shows contamination at levels that could make people very ill from contact.
A medical officer of health, Ramon Pink, says recreational activities like fishing, kayaking, rowing and surfing should be avoided.