Bream Bay beaches roll out smelly red carpet

Decaying algal bloom is getting up people's noses at at Uretiti. Photo / Michael Cunningham

The weather and the tide have conspired to make sure a decaying red carpet of algae gets right up people's noses at Uretiti and Ruakaka.

Patches of soft, fibrous, seaweed-like matter rotting at the high tide mark have been making their presence felt for several weeks in places along Bream Bay .

A slurry floating on the surface near the shoreline is giving a reddish tinge to the water and leaving a crust of pink floss where it gets left on the sand.

While the tides are not enough to wash the substance away, light onshore breezes are doing a terrific job of wafting the pungent smell over nearby homes and holiday camps.

The dying, drying, stinking material is a natural phenomenon often seen in Northland in summer.

It is not toxic to people or animals, a Northland Regional Council (NRC) spokesman said.

Nor is the problem as bad as it was the year before and, in this summer's sweltering temperatures, the crimson tide has not always been a deterrent to swimming.

It comprises a mix of algae that usually live on the seabed, dislodged by water currents and forming mats on the surface where it blooms - photosynthesises and multiplies in the sunlight.

When still on the surface the bloom is alive and it can also survive for some time on the beach when moisture is trapped in the wet sand under the mat's crusty surface.

But it is killed by fresh water so this week's stink is largely the result of last week's rain killing off a fresh dump before the next tide could take it back out.

There have been no easterlies or tidal conditions that might wash the beach clean.

NRC group manager of regulatory services Colin Dall said that after complaints, mainly about the smell, staff had inspected a couple of sites at Uretiti and Ruakaka and did not consider the bloom or its fibrous residue a problem, at this stage.

While the algae is not toxic in itself, people are advised to use common sense and not swim in creeks and lagoons contaminated by dead algae where low water flows have been unable to flush it out.

In the increased sunlight the algae continues to grow and undergo photosynthesis and "bloom", creating giant, red blobs which eventually washes ashore. It is only when it dies that it begins to rot, and smell.

The northern part of the 22km-long Bream Bay is less affected than Waipu Cove in the south was earlier this summer.

Driven by the stench and unsightly red carpet, in January residents and other beach users triggered a standing NRC resource consent to remove tonnes of dead algae from the sand.

Four local farmers moved tonnes of algae that had begun to build up from Christmas Eve.

The clean-up took about six hours and covered about an 800m stretch of beach. The algal-laden sand was taken to a council-approved site the next day.

Had the work been charged out, it would have cost about $4000, but nowhere near the $16,000 price tag for the bigger clean-up the year before.