Warning signs were put up at Waiinu beach in January after a single sample of freshwater emerging on the sand was found to have abnormally high levels of faecal coliform bacteria.

The water emerging from a swamp there forms shallow pools, and children often play in it.

South Taranaki District Councip put up signs on January 15, warning people to stay clear, communications manager Gerard Langford said.

Since then levels have been satisfactory, and the signs were to be taken down yesterday.

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The highest level of the bacteria was found at the southeastern end of the beach. The source is unknown and could have been animals, birds or humans.

South Taranaki District Council is leading the investigation into the cause.

The investigation may move farther afield, because high bacteria levels have been found in several freshwater springs above the beach - springs that are also used as swimming spots, Taranaki Regional Council environment quality director Gary Bedford said.

No one has taken ill due to contact with the water, as far as Mr Langford knows. And nearby seawater was well within health limits, as it has been for 20 years.

Waiinu campground custodian Mick Zimmerman said it has been very busy this summer, despite one area being fenced off due to sodden ground.

The bacterial contamination at Waiinu in January follows high bacteria levels found in the Mowhanau, Kai Iwi and Ototoka streams further down the coast at the same time.

Coastal streams are susceptible to things like run-off from farming, Horizons Regional Council science manager Abby Matthews said.

"When they're not getting much water running through and it's warm humid weather it's ideal conditions for bacteria to grow."

Summer downpours wash in excrement from sheep, cows and birds.

"In coastal streams, you do seem to see these sorts of results pop up. If I have a choice between swimming in a coastal stream next to a beach or swimming at the beach, I would always choose the beach."