The spillage of more than 150,000 gallons of diesel oil from an Ecuadorean tanker near the Galapagos Islands is a "catastrophe", the environmentalist David Bellamy has warned.
The spill, covering 186 square miles, threatens the delicate ecosystem of the islands famous for their giant tortoises and rare species.
Floating nets and barriers have been installed to control the spill, but there are fears that the fuel could sink to the ocean floor, destroying algae, a vital key in the food chain.
Charles Darwin developed his theory of evolution while studying wildlife on the islands.
Mr Bellamy, who is president of the Galapagos Foundation, says: "Here you have a unique series of ecosystems which are under immense pressure anyway, over-grazing, too many fires ... It is a catastrophe, it shouldn't have happened."
Mr Bellamy says he hopes the slick could be contained and the environmental damage minimised.
"As long as the oil can be contained and kept from the most important beaches, then that catastrophe can be alleviated," he told BBC Radio 4's The World at One programme.
The emergency started when the tanker Jessica, carrying about 243,000 gallons of fuel, ran aground last Tuesday in a bay on San Cristobal Island.