Environment Waikato is reporting an upsurge in illegal dumping of animal and fish waste into fresh water on the Coromandel recently.
Investigations and complaints manager Patrick Lynch said the council had received about a half dozen reports of such dumping in the past few months.
The materials dumped in fresh water have ranged from skinned possums to filleted fish.
"This sort of thing produces an unsightly mess and can contaminate water with bugs that cause illness," said Mr Lynch.
"It is illegal under the Resource Management Act to dump these types of contaminants into water."
Mr Lynch urged people to dispose of animal and fish waste responsibly, and asked the public to continue to report any illegal dumping on the EW free phone 0800 800 401.
More information on rules covering dumping is available from EW on 0800 800 401.