The Bellingham Herald reports the young adult male weighed about 110 pounds and showed no obvious signs of injury or disease.
The big cat's carcass was found Friday by a man walking on Squalicum Beach.
Wildlife Officer Ryan Valentine speculated it may have eaten something poisonous or possibly drowned. It's unusual to find a cougar on a beach but the predator may have been looking for deer, using Squalicum Creek as a travel corridor.
The department says the carcass was taken into the hills for disposal.