HONG KONG (AP) _ An oil spill from a tanker collision earlier this week could further threaten a highly endangered species of dolphins in Hong Kong, environmentalists said Friday.

Some 8,100 cubic feet of heavy oil leaked into the sea north of Hong Kong's Lantau Island after a small Chinese oil freighter collided with a Norwegian vessel and sank early Tuesday. A brown-colored oil slick covering an area of 107,640 square feet had drifted near the northern coast of Lantau and some had reached the Sha Chau marine park, a dolphin sanctuary, said Raymond Tam, a Marine Department spokesman.

Tam said the slick had been largely cleaned up by Thursday. The Marine Department planned to work on cleaning up the shore near the marine park on Saturday, he said.

Although no dolphins had been found dead so far, the animals could suffer from exposure to the oil and from a lack of food as the pollution hits the food chain, said William Cheung, a conservation officer of the World Wide Fund for Nature.

Chinese white dolphins inhabit the seas north of Lantau island, to the west of the city. There are now between 80 to 150 Chinese white dolphins living in Hong Kong waters, according to the World Wide Fund for Nature.