Contaminants from a business in Napier spilled into the Tyne St drain, which flows into the Ahuriri estuary yesterday - turning the water murky.
The Hawke's Bay Regional Council was alerted to the incident at 1.30pm and were on the scene soon after.
Yesterday afternoon, the council's environmental officer of
compliance, Ian Lilburn, said "the current spillage had stopped".
"The regional council is doing everything to minimise the impact on the environment, including liaising with the company involved with the spill to ascertain how it happened and how to prevent such a thing from happening in the future."
Mr Lilburn said he did not believe the spill was deliberate and the incident was under investigation.
"It is possible something has gone wrong with a valve or processes."
He said he was not in a position to name the business involved but it was not a nearby tannery.
Control gates were dropped to contain the spill and a truck was used to clean and suck the drain. A boom was also placed in the water to stem the flow into the estuary.
"The Public Health Unit assessed the risk to public health and believe it is very low, as it doesn't contain effluent or serious chemicals," Mr Lilburn said.
He encouraged people who saw such a spill to phone the council's pollution hotline on 0800 108 838.
"By midday tomorrow, the regional council will reassess the impact and anticipate the clearing to be completed by then."
A Napier local said he saw "brown muck" seeping through at 8am yesterday and it had increased by noon.
"It smelled like a tannery and the fish were all over it."
