It's that time of year when hundreds of samples start being taken from Northland's most popular beaches, rivers and lakes to check they are safe for swimming.
Summer water quality tests begin later this month and run until the end of March.
The Northland Regional Council has been monitoring bacterial levels at popular swimming spots over summer for more than a decade.
John Ballinger, Environmental Monitoring Programme Manager, said hundreds of samples would be taken from 47 coastal and 12 freshwater sites to check bacterial levels.
The results will be posted online every Friday at www.nrc.govt.nz/swimming.
Mr Ballinger said samples were given one of three grades depending on the number of bacteria in them: They are "green" (suitable to swim), "amber" (potentially unsuitable for swimming) or "red" (unsuitable).
As well as being posted online, the weekly results are forwarded to all three district councils, the Northland District Health Board and other interested parties.
Where results show elevated bacterial levels within 24 hours, it is the health board's and district council's responsibility to take action.
That action might involve further site checks to establish the source of contamination, warning the public not to swim or gather shellfish there, and putting up permanent warning signs at the worst sites.
Mr Ballinger said that most popular spots the council monitored were usually safe.
There are four simple tips as a rule of thumb to judge water quality: Don't swim where there are warning signs indicating unsafe water; don't swim for two or three days after heavy rain; don't swim if water looks dirty/murky, smells or has scum on its surface; be aware of potential sources of contamination both nearby and upstream.
Anyone wanting to report concerns about water quality can contact the regional council's freephone 24/7 Environmental Hotline on 0800 504 639.