Some U.S. scientists believe a killer whale that washed up off the coast of Washington last month might have been killed by a military explosion.

The three-year-old female orca was a member of L-pod, a group that lives in Canadian waters during the summer months.

The killer whale’s carcass washed ashore at Long Beach, Wash., Feb. 11.

A necropsy found the marine mammal died from highly unusual injuries.

"The entire body showed evidence of massive blunt trauma, some sort of pressure wave that was very blunt in nature not the pointed bow of a ship or anything," said Ken Balcomb, senior scientist at the Center for Whale Research at Friday Harbour, Wash., about 15 kilometres east of Victoria.

Balcomb suspects the animal was killed by an explosive device, one of 96 the U.S. Navy deployed in the area in 2011.

"I suspect she died in U.S. waters. And probably from an explosion," Balcomb said. "We're seeking information about what explosions at least the navy would be aware of."

He said he's worried that ongoing naval exercises could wipe out entire pods, including the fewer than 90 orcas that make up the endangered resident population in the southern end of Georgia Strait and in Juan de Fuca Strait, between Vancouver Island and Washington’s Olympic Peninsula.

Seals also killed

Balcomb said 38 seals died from similar injuries last year, and he says a final body count from L-Pod won't be known until it returns to the Juan de Fuca Strait in July.

"Chances are some other whales got killed too," said Balcomb.

The scientist said he hopes an investigation by the U.S. National Marine Fisheries Service will get access to the Navy's classified documents on its activities.

However, a spokesperson for the U.S. Navy denies it conducted any exercises using explosives in the area in February.

The Royal Canadian Navy told CBC News it did use sonar in the Strait of Juan de Fuca Feb. 6, but that no marine mammals were in the area at that time.

But some environmentalists are not satisfied.

"We'd like the navy to release the data on what they were doing," said Jay Ritchlin, of the David Suzuki Foundation.

"We'd also, basically, just like them to understand and acknowledge that this is a critical habitat for these whales and should be designated as off limits for this kind of sonar training."