Swimmers were told to get out of the water at Muriwai Beach near Auckland today after a report of a shark.
Lifeguards believe it was a false alarm and may have been Maui's dolphins that were swimming in the area, which was the site of a fatal shark attack last Wednesday.
Muriwai Volunteer Lifeguards chairman Tim Jago said a board rider reported seeing a small shark, about 1-2m long, at Maori Bay, next to Muriwai, about noon.
Swimmers and surfers were asked to get out of the water while lifeguards deployed a boat to investigate.
Other board riders then told lifeguards they had seen two Maui's dolphins, the world's rarest and smallest known subspecies of dolphin, in the same area a short time earlier.