With the hot weather set to continue almost all the monitored popular swimming spots in Northland have been deemed safe for a much needed dip to cool down.

Northland Regional Council tests 46 coastal and 14 freshwater locations across the region weekly over summer.

The testing for bacteria gauges the risks of people contracting gastrointestinal and other infections in sites used for swimming, water sports and other forms of recreation.

The results are posted on the Can I Swim Here? section of the Land, Air Water Aotearoa (LAWA) website.

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The Northland sites were last sampled on January 3 and all but three sites were marked green, which means suitable for swimming.

Only the Whangārei Falls was marked yellow, which means caution advised, and Piroa Falls was marked red which means unsuitable for swimming.

Omapere on the Hokianga Harbour is also marked red based on its overall bacteria risk, but just along at Old Wharf Rd in Omapere has the green light.

Northland Regional Council coastal and water quality field operations manager Ricky Eyre said as faecal indicator bacteria generally enters the rivers and coast as runoff during rainfall most sites would be expected to be green following the dry period the region has been experiencing.

"So long as the dry weather continues most sites should remain green."

Last week the number of sites which were yellow or red was higher and Eyre said a factor in that was the rain that fell a number of days before the sampling.

"We have had extended dry weather since and the subsequent results have reflected this."

The weekly results are also forwarded to the Whangārei, Far North and Kaipara district councils, the Northland District Health Board (DHB) and other interested parties.

Eyre also provided an explanation for the Whangārei Town Basin water staying brown for more than a week to start the year.

"For starters, the (Whangārei) harbour has a long retention time, meaning it takes a long time for water to leave the harbour so any sediment that enters the harbour can slosh back and forth for some time."

He said the colour and clarity can also be affected by higher levels of plankton in the water which is present over the summer months.