The annual summer water quality tests have begun at Northland's popular beaches, rivers and lakes.
The Northland Regional Council (NRC) tests for bacteria to gauge the risk of people contracting gastrointestinal and other infections while swimming or during other forms of recreation.
During the testing period, hundreds of samples will be taken from 46 popular coastal sites and 13 freshwater locations, with results posted on the national environmental reporting website LAWA - www.lawa.org.nz.
Last summer 99.1 per cent (606 out of 611) samples at coastal sites and 89.4 per cent (161 out of 180) of samples at freshwater sites over summer met national ''guideline values'', meaning they were considered safe for swimming.
The results are forwarded to the Whangarei, Far North and Kaipara District Councils, the Northland District Health Board (DHB) and other interested parties.
"The DHB and relevant district councils are also informed of any results showing elevated bacterial levels within 24 hours and it's then their responsibility to take any further action required," NRC chairman Bill Shepherd said.
That action can include further site investigations to establish the source of contamination, public warnings not to swim or gather shellfish or putting up warning signs.
The summer testing regime resumed last Monday and will run until February 21.
Mr Shepherd said people can cut down any risk of infection by staying out of the water for two or three days after heavy rain which could carry run-off from land or where there are warning signs. They should avoid swimming where water has scum on the surface, is discoloured or smells.
Water quality concerns can be reported to the 24/7 Environmental Hotline on (0800) 504 639.