The Otago Regional Council said on Thursday the spill involved 400 to 600litres of diesel entering the harbour from the South Dunedin stormwater network.
Council compliance manager Tami Sargeant said the council was following up on a lead provided by a caller to the council’s pollution hotline on Thursday.
The council had that day appealed for anyone with information about the damaging spill to contact them.
"We cannot say at this stage whether the spill is likely to have been deliberate, but given the volume of diesel involved we suspect that someone near the source of the spill would have been aware of it," Ms Sargeant said yesterday.
"Until we confirm the source of the diesel, we are still keen to hear from others and encourage them to get in touch," she said.
The diesel was continuing to discharge and make its way to the harbour via the outfall pipe and this was considered a serious breach of legal requirements.
The time it took for the diesel contamination to flush from the network depended on how much rain fell, but it was likely that it would continue discharging over the coming days.
Booms had been placed at the stormwater outfall into the harbour to soak up as much of the diesel contamination as possible and stop it from flowing further into the harbour.
The booms would be changed daily at low tide until the diesel stopped discharging, she said.
Frank Aluesi, who lives nearby and fishes regularly in the area, said he remained concerned that pollution continued to enter the harbour, damaging the environment and threatening both fish and the people trying to catch them.
