Popular Welcome Bay swimming spot Kaiate Falls has been labelled unsafe after faecal coliform bacteria was found in the water.

Medical officer of Health Dr Jim Miller says he doesn't know what is causing the high levels of contamination, and is not sure how long the warning will persist.

The popular summer swimming hole at Kaiate Falls is currently unsafe for swimming.

Jim says: 'The history is poor, but without specifics that's the sort of area where there might be quite a bit of agriculture or stock access, a lot of birds or septic tanks, or on site disposal.

'It could be any one of a number of those thing causing a problem in the meantime.”

If the high bacteria levels continue, regional council staff will be asked to look for the cause upstream.

'If it continues much longer, I would certainly be asking them to have a look and see if there is a reason for it,” he adds.

The Kaiate Stream headwaters originate in bush a relatively short distance away in the Papamoa hills. The main stream crosses a kilometre or so of farmland before flowing beside the road for a short distance.

Some rain would usually clear the problem says Jim, but that's something that isn't forecast in the near future.

He says there's always some faecal coliform bacteria in natural waters, but its more about the levels.

'People could actually get ill swimming in water at that sort of level,” says Jim.

Kaiate Falls is the only popular bathing spot in the Western Bay of Plenty to receive the public health warning.

The warning is based on an overall assessment or grading to provide a level of background risk, plus the results from sampling. The BOP Regional Council is sampling Kaiate Falls' water daily while the warning is in effect.

The background checks apply to all popular bathing areas in the Western Bay, including harbours, beaches and rivers.

'There's an overall assessment or grading and that gives a kind of a background risk,” he says. 'It doesn't mean on any particular day it's going to be safe or unsafe to swim in that particular location. It just means that some places are inherently safer than others.”

The council bases the background risk on things in the catchment that can cause a problem; wastewater from a water treatment plant, birds and areas where stormwater can get into the catchment.

'In some places, it may not be a great idea to swim anyway because of the environmental issues,” says Jim.

'People have to keep their eyes open. If places are mucky, or if there's been heavy rain, don't go. And if it looks unclean, perhaps go somewhere else.”

Another popular swimming spot, the Wairoa River, was last sampled in December.