The wasp population has exploded along Hawke's Bay riverbanks.
It is not known why wasps have increased to such large numbers in these areas but there have been reports of similar problems in other parts of the country, Regional Council rivers manager Vince Byrne, said.
"If there's a large amount of wasps around, our advice is to leave the area, and certainly avoid going into the undergrowth where you may disturb a wasp nest,"
Wasp stings are painful and can result in severe allergy reactions which may require immediate medical attention.
The Regional Council is warning people to take care along river berm areas and to watch where their dogs go.