A gray whale seen swimming injured through Puget Sound for about two weeks likely died from a collapsed lung or infection that trapped air in its body and prevented it from diving, experts from the Cascadia Research Collective (CRC) say.

National Oceanic and Atmospheric Administration (NOAA) officials said last week that researchers completed a necropsy of the juvenile gray whale Thursday afternoon. The results of the procedure showed the animal was “clearly emaciated,” and had air in the tissue under the blubber layer in the chest cavity, an expected result, researchers said, given its condition when alive. One lung was also apparently filled with fluid and slightly deflated.

According to a NOAA statement, the whale was first sighted on April 24 off Kingston, Washington and was active and swimming but appeared to be unable to dive. NOAA Fisheries crews were sent to the scene to observe the whale. Then, on April 30, CRC and Washington Department of Fish and Wildlife’s Marine Mammal Investigators were able to determine it’s approximate age and size: 35 feet long and likely a juvenile that was only a few years old.

On May 6, CRC, Washington Department of Fish and Wildlife and the Seattle Aquarium conducted a secondary health assessment, NOAA officials said. The whale’s back showed sun damage and blistering from being exposed at the surface. Biologists and veterinarians suspected it may have been suffering from an infection that produced gas inside its body or a collapsed lung that had filled its chest cavity with air.

“Either condition could have made the animal too buoyant to dive. Because gray whales feed by diving to the sea floor and sifting sediment for small marine organisms, such as tiny crustaceans, the animal’s injuries compromised its likelihood of survival,” NOAA officials said in the Friday statement.

NOAA continued to montor the whale, but did not intervene because of the danger a distressed whale can present.

“The tools do not exist to either treat or euthanize large, free-swimming marine mammals,” according to NOAA.

The whale was spotted throughout Puget Sound, including near Vashon Island, West Seattle and Tacoma.

On May 8, the whale was found dead in Elliott Bay off downtown Seattle, but it subsequently drifted north. The whale was located and towed to Indian Island, a U.S. Navy site on May 11.

The whale’s tissues will be examined further as researchers work to determine exactly what caused it’s death.

This is the second whale death in the Puget Sound region recently. A gray whale was found dead off the coast of Vashon on April 19. It was determined that the whale likely died from starvation and was a “normal occurrence,” as four to eight whales usually die every year in Washington.