ANCHORAGE, Alaska (AP) - An underwater pipeline that sprung a leak in Alaska's Cook Inlet, an area known for diverse marine life, probably dumped less than three gallons (11 liters) of crude oil into the ocean, the pipeline's owner said Monday.

The spill between two production platforms owned by Hilcorp Alaska LLC was spotted Saturday. Cook Inlet stretches 180 miles (290 kilometers) from the Gulf of Alaska to Anchorage and is home to an endangered population of beluga whales.

Hilcorp by Sunday had removed all oil from the 8-inch (20.3-centimeter) diameter pipeline.

FILE- In this Feb. 12, 2016, file photo, the Chugach Mountains and the buildings of downtown Anchorage, Alaska, are reflected in the still waters of Cook Inlet. Oil from an underwater pipeline leak was discovered in the inlet on Saturday, April 1, 2017. The owner of the underwater pipeline, Hilcorp Alaska LLC, says the volume of the spill is estimated to be less than three gallons (11 liters). In three flyovers Sunday and a final one Monday morning, no additional sheen was spotted from the air. (AP Photo/Mark Thiessen, File)

Cook Inlet is also habitat for humpback whales, the western population of Steller sea lions and northern sea otters. Harbor seals, killer whales and porpoise use the inlet.

The Kenai Peninsula makes up the eastern side of the inlet and draws thousands of anglers every summer seeking halibut in the inlet or salmon in ocean water and streams.

The spill volume was estimated from the size of sheens that were seen, said company spokeswoman Lori Nelson in an emailed response to questions. The sheens dissipated, Nelson said.

In three flyovers Sunday and a final one Monday morning, no additional sheens were spotted from the air.

Hilcorp, the Coast Guard and state environmental authorities over the weekend formed a unified command in response to the spill that was suspended Monday, said Candice Bressler, spokeswoman for the Alaska Department of Environmental Conservation.

The leak's cause was unknown.

The leak is the second in Cook Inlet this year for Hilcorp Alaska, a subsidiary of Houston-based Hilcorp.

In an unrelated incident, processed natural gas continues to spew into the inlet from an underwater pipeline that supplies four other production platforms.

The platforms burn natural gas for power. That leak was discovered in February and company officials estimate it has been leaking since mid-December.

Hilcorp says the gas leak will be repaired after floating ice no longer poses a threat to divers who would perform repairs.

The oil leak was discovered Saturday when workers on the Anna Platform "felt an impact," according to the DEC. They spotted an oil sheen and bubbling in the water near one of the platform's legs.

The suspected leaking line connects Anna Platform with Bruce Platform in 75 feet (23 meters) of water.

The 1.6-mile (2.6-kilometer) line has a capacity of 19,362 gallons (73,291 liters) and was full. Hilcorp Alaska shut down the platform and lowered pressure in the pipeline to zero.

Overflights spotted six sheens. The largest was 10-by-12 feet (3-by-3.7 meters).

Bressler said Hilcorp used a polyurethane "pig," a device inserted into the pipe, to push remaining crude oil toward the Bruce Platform. It was processed and moved to a tank farm.

Hilcorp has detected no harm to wildlife, Nelson said.

This photo provided by Cook Inlet Spill Prevention and Response, Inc. shows pan pan ice taken during an agency overflight near a Hilcorp Alaska LLC offshore platform in Cook Inlet, Alaska, Monday, April 3, 2017. Officials said an underwater pipeline spill between two production platforms owned by Hilcorp dumped less than three gallons (11 liters) of oil into Cook Inlet. (Derek Samora/CISPRI via AP)