Since May 2015, the carcasses of 11 fin whales, 14 humpback whales, one gray whale, and four other whales of indeterminate species turned up along the western Gulf of Alaska, according to the National Oceanic and Atmospheric Administration (NOAA).
NOAA declared the cluster of whale deaths "an unusual mortality event" on Thursday, triggering a formal agency inquiry into the strandings that will bring together federal and local experts in a specially funded team.
"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," said Teri Rowles, a NOAA marine mammal health and stranding response coordinator.
A leading hypothesis for the cause of the deaths, NOAA fisheries spokeswoman Julie Speegle said, is that they may be linked to a toxic algae bloom in the Pacific Ocean along the US West Coast that has led to the closure of shellfish harvests in Washington state, Oregon and California.
The bloom, which first appeared in May, involves microscopic algae that produce a neurotoxin potentially fatal to humans called domoic acid.
The 30 whales found dead so far this summer washed ashore along a span of coastline stretching more than 1,000 miles (1,600 km) from south of Anchorage to the Aleutian Islands.
To date, the strandings tally amounts to almost three times the historical average for such whale deaths in the region, NOAA said.
The most recent whale carcass in the group was found in mid-August, according to Speegle.
The formal investigation was expected to begin as early as September, and could take months, even years, of data collection and analysis, she said.