It appeared a vehicle had run through the park, tearing up bits of the turf on the lower terrace early on Saturday.
The council's recreation manager, Erik van der Spek, said the cost of the damage was unknown, but he imagined it would cost hundreds of dollars to fix.
He called the damage disappointing and it was another cost to Waitaki ratepayers.
He said the damage occurred on pitches being used by football teams so it would be difficult to repair them while the winter sports season was in progress.
"Obviously trying to get new grass to establish itself while they're using the fields would be rather difficult.''
He said if a field was repeatedly damaged it became a lot harder to fix.
While work could be done to repair the surface damage the ground below could change and become compacted.
"That would take tens of thousands of dollar to fix.''
Oamaru police (03) 433-1400 or Crimestoppers 0800 555-111.
