Surfers and beach-goers at Sandy Bay, 41km north east of Whangarei, have been surrounded by brown waves after a macro-algae bloom was suspected of breaking down and causing the discolouration in recent weeks.
The water in the bay went from a reddish colour, around Christmas, to brown and Northland Health officials have taken water samples to see if the harmless bloom contains anything that could be toxic to beach-goers.
Ricky Eyre, from the Northland Regional Council, said algae can bloom in the warmer summer waters to very high concentrations that discolour the water as seen at Sandy Bay.
The results have come back and there's nothing nasty lurking below the brown tide, Mr Eyre said.
The results show a high biomass of brown macro-algae was dominant and no toxic species were detected.
Sandy Bay is a popular beach for swimmers and surfers.
