(Reuters) - Alaska officials reported an oil leak from an underwater pipeline late on Saturday that was within habitat designated as critical for endangered Cook Inlet beluga whales.

The leak originated from an eight-inch pipeline connecting two Hilcorp Energy production platforms in the Upper Cook Inlet. Hilcorp shut down both platforms following the leak and the pipeline is now operating at reduced pressure, the Alaska Department of Environmental Conservation (ADEC) said.

Hilcorp estimated that fewer than 10 gallons of oil have been released, but ADEC has not confirmed that figure, spill prevention and response director Kristin Ryan said on Sunday.

“We do not know if it’s still leaking,” Ryan said.

“The reduced pressure should minimize the amount being released from the leak and we have not seen sheening since that time, but we have not been able to confirm.”

Hilcorp did not immediately respond to a request for comment.

The population of belugas that swim off the coast of Alaska’s largest city was listed as endangered in 2008 by the federal government and more than 3,000 square miles have been protected as critical habitat since 2011.

The spill occurred in an area that is also home to other endangered mammals including the Steller sea lion and the humpback whale.

The ADEC has not seen any impact to wildlife yet. Three overhead flights were conducted on Saturday with no animals seen where sheening had occurred or near the pipeline, Ryan said.

The cause of the leak was unknown and being investigated, ADEC said. The line can hold 461 barrels of oil at full capacity.

Hilcorp last week shut two Alaskan oil production platforms after reducing pressure on a leaking natural gas pipeline in Cook Inlet. [nL2N1H50Z5]

The two incidents are unrelated, ADEC said.

The Center for Biological Diversity said in a statement on Sunday it had sent Hilcorp a 60-day notice of its intent to sue for the gas leak, and is monitoring the oil leak to determine whether additional legal action is warranted.

“We’re really worried about what this means for Cook Inlet belugas with the double whammy of an oil spill and gas leak in the same season,” Miyoko Sakashita, oceans program director for the Center for Biological Diversity said in an emailed statement.

Hilcorp has hired a diving contactor to investigate the line and make repairs and it is anticipated that this work can be conducted late next week, ADEC said.