It appeared paint was tipped into a roadside drain and a culvert, with Saturday’s rain spreading it along about 500m of the estuary, Pihema said.
He thanked campground staff who raised the alarm as soon as they saw the spill.
Pihema urged people not to tip paint - or any other substance - into the stormwater system.
Many stormwater drains empty directly into the ocean.
Pihema advised people not to gather shellfish in the area for three days as a precaution.
The nearby Te Haumi tidal flats were “huge” for shellfish gathering, he said.
“We’re lucky in this case it was paint. It could have been a lot worse.”
Pihema said the incident highlighted a broader issue of illegal dumping.
Much of the area is a flood plain, so rubbish and dumped substances eventually end up in the Bay of Islands.
“We have to do the right thing, not just for the environment, but for our children. The damage we do now is going to catch up with future generations,” Pihema said.
Northland Regional Council regulatory services group manager Colin Dall said dumping paint or paint wastewater was “poor and inconsiderate behaviour”.
“It was dumped in a drainage channel close to the estuary and was always going to end up being flushed into the estuary, given the weather conditions at the time.
“It is inexcusable and disappointing that there are still people that have no regard for the environment and the adverse effects of their actions,” Dall said.
Anyone with information about who was responsible is urged to contact the regional council.
