It's understood it was in the area near the Tyne St waterway.
Council staff responded and were on site within half an hour of being notified early last Tuesday night.
The staff took samples and initiated investigations to determine the cause of the pollution, and staff had since conducted interviews by phone with business operators and witnesses of the recent environmental incident.
"We are awaiting the sample results to confirm the contaminant and concentration levels," staff said.
"We hope that this will provide enough additional information to ascertain the pollution source and act accordingly."
Further work had been done to determine whether there had been any adverse effects from the contamination, with staff having to observe all the rules of social distancing and other Covid-19 alert requirements.
The council says members of the public should report any sort of pollution in the city's urban waterways by calling 0800 4 NAPIER and ask to speak "urgently" to a member of the Environmental Solutions Team, so that action to limit pollution could be taken immediately.
"Putting it on Facebook is not effective in fixing the problem or alerting us to the fact, so please call us or the Regional Council's Pollution Hotline as quickly as possible," the Council says.
Staff says the precautions officers have to take during the Covid-19 crisis complicates their work further, but they are "totally committed to rectifying these types of problems and ensuring pollution incidents to our urban waterways are dealt with immediately to ensure those who take advantage of our environment are held to account."
Recently the council initiated an intensive education campaign to show the people of Napier that what goes on the ground goes to the sea, as anything that lands on the ground and gets washed by rain, or spilt upon concrete areas ends up in the Ahuriri Estuary (Te Whanganui-a-Orotu) or the Pacific Ocean.
Further information is available at https://www.napier.govt.nz/services/stormwater/how-you-can-help/