An alarming number of gray whales have been found dead this year from Mexico to Alaska, triggering a federal investigation into what’s causing the die-off.

NOAA has declared an “unusual mortality event” for gray whales on the North American west coast and launched an investigation.

Grey whale (Eschrichtius robustus) found beached near the Placer River along Turnagain Arm is one of five grey whales reported dead along the Alaska coast during 2019.

NOAA is monitoring significant numbers of gray whale deaths this spring along the Pacific coast.

Researchers say the population of gray whales off the West Coast of the United States has fallen by nearly one-quarter since 2016, resembling a similar die-off two decades ago.