Over the last few months, at least 30 whales have perished on or near the shores of the western Gulf of Alaska.

On Thursday, the NOAA declared the die-off an "unusual mortality event," triggering a federal investigation into what exactly is causing the deaths.

"NOAA Fisheries scientists and partners are very concerned about the large number of whales stranding in the western Gulf of Alaska in recent months," Teri Rowles, NOAA Fisheries' marine mammal health and stranding response coordinator, said in a press release.

In Canada, government officials made a similar declaration, promising their scientists would cooperate with American investigators.

"We're working closely with NOAA to analyze samples," Paul Cottrell, scientist and program director with the Department of Fisheries and Oceans Canada, told reporters.

The deaths include those of 11 fin whales, 14 humpback whales, one gray whale and four unidentified whale species. More dead whales have been found along the coast of British Columbia.

Because the coasts of Canada and Alaska can be difficult to access, researchers are calling for help from citizen scientists.

"While we do not yet know the cause of these strandings, our investigations will give us important information on the health of whales and the ecosystems where they live," Rowles said. "Members of the public can greatly assist the investigation by immediately reporting any sightings of dead whales or distressed live animals they discover."

Marine biologists have suggested a large toxic algae bloom off the coast of the Pacific Northwest could be to blame, but a concrete connection has not yet been established. Scientists say they'll continue to test water and whales for heightened levels of harmful bacteria, viruses or other biotoxins.

"Biotoxins will be one of the top priorities, but not the only priority that we'll be looking at to rule in or rule out whether it's playing a role in this death investigation and these mortalities, both in Canada and the U.S.," Rowles told the Alaska Daily News.

It's been a strange and deadly summer for a variety of species up and down the West Coast. Among other odd events, Pacific beaches have witnessed stranded sea lions, dead seabirds and tuna crab invasions.