The Department of Conservation advises people in Mahia in the Hawke's Bay to avoid a well-known dolphin, Moko, who is likely to become more aggressive.
A swimmer had to be rescued in July when Moko kept her from returning to shore.
DoC says the dolphin has grown out of a playful childhood and now needs to seek companionship with another dolphin.
Professor Mark Orams, of Auckland University of Technology, says dolphins are not able to differentiate in their social networks between humans and their own kind.
He says Moko needs to be left alone, as he is less likely to mix with other bottlenose dolphins if he continues to interact with people.