Dairy cows have been blamed for high E coli levels which have forced the closure of popular Patea River swimming holes in Stratford for more than a month.

On 1 February 1300 parts of E coli per 100mL was recorded at King Edward Park - well over double the Ministry for the Environment's "unacceptable risk" level, which is 550 parts/100mL.

The "action level" has been exceeded six times since 4 December and signs warning people not to swim, drink from or fish in the Patea River went up later that month.

Taranaki Regional Council is responsible for monitoring the region's water quality.

In a statement, environmental quality director Gary Bedford said DNA testing had found cows were the source of the E coli and the council was investigating above the catchment to locate its origins.

Local Graham Harkness said he could not believe people were not allowed in the river.

"It's amazing because we used to catch freshwater crays, have fires on the bankside [and] cook freshwater cray -koura - and roast spuds and so forth.

"[We could] swim without any concern about our health and safety."

Photo: RNZ / Robin Martin

Aucklander Molly Kroon usually swims in the river when she comes to visit her grandmother, but not this year.

"We came down to grandma's farm every holiday and then we'd come down to the swimming pools and sometimes take a dip."

She found the warning signs upsetting.

"It's quite sad because I used to love being in the water but now I just feel kind of gross. I wouldn't get in there now."

Mr Harkness laid the blame firmly at the feet of farmers.

"I'm pretty sure it's because of overstocking. They're just putting too many animals on what the land can naturally take and they're using bought in feed to make the situation worse," he said.

"I know we hear all the things that they're doing [to make things better] a lot but it's obviously not enough."

Federated Farmers provincial president Donald McIntyre said the area above the catchment was dairy country but that did not mean any one farmer was at fault.

"The source point is probably of more interest ... because you've got to remember in recent times we've had some high intensity rainfall so it could be across land rather than a discharge from a treatment facility."

Mr McIntyre, who is also a regional councillor, said he trusted the council to track down the problem and take the appropriate action.

In the past, the council has fined farmers in breach of their effluent treatment consents tens of thousands of dollars.

Environmental activist Sarah Roberts was less than impressed with the regional council's water quality testing regime over the summer.

"I'm quite concerned because it's been known for quite some time that there are issues with the water here," she said.

"The signs went up late December but right from early on when they were testing there were high E coli spikes and big gaps in the testing."

There was no testing done at King Edward Park between 8 December and 10 January.

The council said efficient use of staff resources meant both the fresh and coastal water samples were taken on the same run, and testing criteria for both were not met during that period.

Photo: RNZ / Robin Martin

Despite the warning signs, dog walker Tricia Jamieson had no qualms about letting Kano and Loki into the river.

"I'm comfortable to let these guys in here because this is flowing water and the problem is the standing water where the ducks are and the bacterial contamination is," she said.

"I bring these guys down everyday and they don't have any problems."

E coli can cause diarrhoea, stomach pain or cramps, flu-like symptoms, nausea and vomiting.

If people believed they had symptoms it was advised to see a doctor.