When John and Judy McCaffery brought their family to Matapouri Bay for a summer holiday they were horrified to find part of the estuary polluted with green algae.

Mr McCaffery said the problem in the southern side of the estuary meant their children and grandchildren could not swim or paddle kayaks.

The algae is attached in the sand and growing long thick scum, sometimes called water silk and blanket weed.

Mr McCaffery said he believed it is caused by fresh or salt water becoming enriched with too many nutrients.

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"Basically, it means the estuary is carrying the maximum load of enriched nutrients and urgently reducing this load is needed to solve the problem."

Mr McCaffery has laid a complaint with the regional council about the algae .

He said that in more than 60 years of visiting Matapouri, he had never known the problem to be so bad.

However, the estuary has been sampled weekly and tested by Northland Regional Council for faecal bacteria since November as part of the council's summer swimming site water quality testing programme, a spokesman said.

The Matapouri tests have consistently shown low levels of faecal bacteria, indicating the water is suitable for swimming and recreation.

The algae is probably Ulva (formerly known as Enteromorpha), or similar, and the only reports the council has received of it in recent times have all been at Matapouri, he said.

The NRC did not consider it to be caused by an increase in nutrient levels.

Algal build-ups are not unusual around New Zealand during long periods of warm, calm weather, the NRC spokesman said.

While green algae are capable of prolific growth, they do not generally pose a health hazard and would eventually be flushed away by rain and higher water flows, he said.

The most spectacular event in recent years has occurred with red algae at Waipu Cove.

The NRC currently holds a resource consent allowing the Waipu community to remove the extremely large build-up as it was a major nuisance there, the spokesman said.

The situation and volumes involved at Matapouri fell well short of that category, he said.

Mr McCaffery described the "wait, see and hope response as totally inadequate''.

"The estuary at Matapouri is considered by all of us on the coast to be the crystal clear, unpolluted safe zone where our kids can safely learn to swim, snorkel and develop care and concern for its marine life. Now it faces ruin as [the algae] is spreading rapidly.

"The outbreak is not just about the presence of bacteria but also about preserving the mauri of the estuary, involving its cultural and recreational values to the local community and preventing its spread to other parts of the estuary," Mr McCaffery said.

The McCafferys will write to the Matapouri Marae committee and Whangarei District Council, pointing out the council's policies to protect Maori values and public recreational areas.