HOMER, Alaska—An environmental advocacy organization is calling for the immediate inspection of all oil and gas pipelines in Alaska's Cook Inlet after two underwater lines broke and leaked in recent months, with one still spewing natural gas into the inlet.

The inlet, home to endangered beluga whales and other species, is the oldest producing oil and gas field in Alaska. Many of the pipelines—including the two that recently leaked—were built in the 1960s.

The Center for Biological Diversity issued the legal petition on Thursday, asking the federal Pipeline and Hazardous Materials Safety Agency and the Alaska Department of Environmental Conservation to inspect the pipelines.

"It's scary to think about how decayed some of the offshore pipelines littering Cook Inlet may be," said Kristen Monsell, an attorney with the center. "These old, vulnerable pipelines pose a toxic threat to the people and wildlife of Cook Inlet."

Both of the pipelines that leaked—one carrying natural gas, the other oil—are owned by Hilcorp Alaska, a subsidiary of Houston, Tex.-based Hilcorp. The company operates virtually all the oil and gas infrastructure in Cook Inlet. Hundreds of miles pipelines traverse under the inlet.

The natural gas leak was first identified on Feb. 7, but has been leaking since late December, according to the company. The pipeline carries almost pure methane from shore to fuel oil platforms along the eastern side of the inlet. The company has said it cannot stop the leak yet, because ice in the inlet has made it impossible to send divers to repair the broken pipe. Further, shutting off the gas flow could result in residual crude oil in the line leaking out, causing an even worse disaster, it has said.

The company is under an order by PHMSA to repair the leak by May 1 or shut it completely.

Hilcorp employees reported a second leak on Saturday from an oil platform on the west side of the inlet after they felt an impact. The leak was stopped within a day, and the company has said only three gallons of oil spilled out. Sheens as large as 10 feet by 12 feet were seen three and a half miles from the platform about an hour after the leak was reported.

The state DEC has said it is investigating the company's inspection records and trying to get answers about the cause of the leaks. According to the Alaska Oil and Gas Conservation Commission, the company is responsible for more than a quarter of all 45 safety violations from 1977 through 2016. It started operating in Alaska in 2012.

"Infrastructure reviews and inspections are a priority, but right now we are fully focused on our response efforts," Kristin Ryan of the Alaska DEC said in response to the request from the Center for Biological Diversity. "We will have more information on an infrastructure review in the future."

The types of annual inspections that Hilcorp conducts on its Cook Inlet pipelines cannot identify whether the pipes have eroded or are dented or gouged—all known problems for pipelines in Cook Inlet.

Cook Inlet is a particularly harsh place for oil and gas infrastructure. It is home to some of the strongest tides in the world. The sand can erode from underneath a pipeline, leaving it dangling above the seabed. Boulders and rocks can get caught in the current, creating a vortex around the pipe that can be strong enough to damage or even shear an 8-inch pipeline like the ones in the inlet.

In 2014, when the gas pipeline was owned by XTO, a subsidiary of ExxonMobil, it leaked twice. In both cases, the leak was stopped quickly because ice was not a factor.