Whanganui District Council is investigating the discharge of a putrid, green fluid into the Whanganui River at the weekend.
As yet the liquid has not been identified or if it has any potential effect on the environment.
A resident, who did not want to be named, sent the Chronicle pictures of the discharge. The fluid was coming from a pipe which runs under the unsealed road between the Army huts and South Beach, and flows into the river.
"We took the photo when many people were at the fishing competition weigh-in at the army compound," the woman said. "The fluid, whatever it was, was a bright green colour but the stench coming from it was disgusting."
She said the discharge accumulated in a tidal pool on the mudflats about 6m from the outfall and well below the high tide mark.