Whanganui District Council is appealing for help from the public to identify who dumped a pollutant, thought to be paint, into a pond at Rotokawau.
The pond is above Virginia Lake in a reserve area in the Rotokawau subdivision.
Stormwater technical officer Brad Haburn said the council was notified about the incident on October 5 and maintenance contractors Veolia used a vacuum truck to remove as much of the polluted water as possible.
"It's likely the pollutant was dumped directly into the pond."
"Council infrastructure staff inspected the upstream stormwater network but no signs of a dumped pollutant could be seen," Haburn said.
"It's likely the pollutant was dumped directly into the pond. To address traces of remaining pollution, we flushed the pond with clean water from nearby hydrants.
"The pollutant appeared to be paint but the source could not be identified. The stormwater drains leading to the pond were dry and had no traces of the pollutant."
Council compliance operations manager Warrick Zander asked anyone who knew about the spill, or who sees anyone dumping anything into the pond, to contact the compliance team on 349 0001 or Horizons Regional Council's pollution line on 0508 800 800.
"We would welcome any further information," Zander said.