The Department of Conservation says a Bryde's whale found dead near Auckland died after being hit by a ship.
Members of the public spotted it floating near Waiheke Island and contacted the Department of Conservation, which recovered the carcass of the female whale on Tuesday.
DoC towed it to Motuihe Island for examination and says that found the whale had been killed when it collided with a vessel.
Spokesperson Phil Brown says Bryde whales are the most commonly sighted whale in the Hauraki Gulf Marine Park.
He advises boaties encountering them to enjoy the experience but to give them a wide berth and keep their speed down while they are around both whales and dolphins.
Mr Brown says there are fewer than 200 Bryde's whales in the Hauraki Gulf.