Greater Wellington Regional Council has been notified of a potential paint spill in Wellington Harbour.
Posts to social media show a white substance near the shore at Balaena Bay.
Greater Wellington spokesman Stephen Heath said they are still trying to understand the nature of the spill.
"In cases like these it's often the case that decorators are pouring waste into the stormwater system. In which case we try to identify the perpetrator. But we've yet to establish what's going on."
A pollution response team will be dispatched to the area in the next hour.