Contamination of a Hawke's Bay pond, which was linked to a child falling ill, has been put down to contamination by cow faeces and birds.

Hawke's Bay regional councillor Paul Bailey said that a child was still sick after swimming in contaminated water over summer and asked whether inflatable play equipment should still be put in the pond.

"Wherever you put more people you will get more chance of illness, and this would be a Ministry of Health thing," Madarasz-Smith said.

"It would be worth testing through summer, particularly if the inflatable goes in, and we will up the testing with Napier City Council.

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"It's a bit difficult in that the inflatable is in a natural area that we can't chlorinate - it's a risk."

The source of the contamination leading to the month-long closure of the pond in February was revealed to the Hawke's Bay Regional Council's environment and services committee this week.

Regional council coastal quality scientist Anna Madarasz-Smith said that between February 12 and February 19 this year, recreational water quality guidelines were exceeded three times.

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The popular Napier water spot was then closed for about a month from February 21, after a high reading of 475 enterococci per 100ml - the safe swimming guideline is 280.

Regular testing of the water followed, including faecal source tracking, but the investigation failed to pinpoint an exact cause of the elevated levels during that time.

Later tests of surface scum in the pond near the inflatable play equipment showed the elevated counts were linked to birds.

Then, on March 7, cow faeces were found to be the source of even higher levels of bacteria from the Thames/Tyne catchment.

"Where was that coming from - that's the big question," said Madarasz-Smith.

She noted that within the last couple of weeks cows had been roaming the estuary and put back onto railway land with the help of animal control, but it was not certain if such activity would have been a contributor.

"We have the sample in with the lab in Christchurch - if it's positive it could have come from downstream and made its way up with the incoming tide - the other possibility is the meat processing plants in the Thames/Tyne catchment."

She said regional council staff were working with Napier City Council staff to understand the wider water quality and movement throughout the Ahuriri Estuary, including Pandora Pond.

Napier City Council director infrastructure Jon Kingsford said the council had proposed a proactive monitoring programme for the Pandora Pond that would allow both councils to determine water quality and suitability for recreation over a full tidal cycle.

"Most exceedances of Enterococci observed in February and March 2018 were either from samples taken on an incoming tide, or after sufficient volumes of rain.

"The monitoring programme proposes to eliminate as many variables as possible (such as different tidal stages, weather, seasons), and seeks to test for other pollutants such as heavy metals and hydrocarbons. "

He said this monitoring would enable levels of contaminants to be trended so decisions about whether the inflatables were installed were based on science.

He added that the council had an open partnership with the Hawke's Bay District Health Board in relation to the Ahuriri Estuary.

"Our environmental health and environmental solutions teams work very closely with the DHB, carrying out health assessments of the estuary and the industrial areas around Pandora.

"We install signs notifying of any public health risk in relation to the recreational use of the Pandora Pond, and the DHB is a key partner in response to any spill event regardless of the source."