Tauranga marine life expert Graeme Butler says leaking oil from Rena, the container ship grounded on the Astrolabe Reef, poses a considerable environmental danger.

The Tauranga Dolphin Company owner says the ship's leak gives cause for concern.

The 236m container ship grounded on the Astrolabe Reef at 2.20am on Wednesday. Since, she has leaked fuel oil stretching in a 2000m strip. Inset: Graeme Butler.

'At this time of the year there are whales in the Bay, we had reports of a blue whale very close to Astrolabe the other day – maybe within a mile or two, there was a whale a and a calf,” says Graeme.

'So yeah I'm worried about the wildlife, I'm worried about the ship being there and I'm worried about how it could have happened and also wonder about the response, because the response on these things is usually pretty slow.

'If the fuel oil escapes out of the vessel, and I understand there is 1700 tonnes of fuel onboard, the implications for the wildlife on the beaches.

'It will have a major impact on the ecosystem if any proportion of that fuel gets loose.

'I think there would be a danger to the birds, a danger to the surface fish.

'It would work its way right through the life web of the ocean.

'The birds would be affected, the fish, the plankton, the coastline, the seals that are on the coast on Motiti Island, the shellfish, the paua – it can't have anything but a serious impact.”