A young beluga whale whose carcass was found in a river nearly 1,000 miles from its natural ocean habitat probably died last fall and remained in the frozen river all winter, according to scientists.

Canoeists found the whale June 9 on the Tanana River in central Alaska, about 40 miles southwest of Fairbanks. The discovery mystified scientists.

Beluga whales often feed on fish in estuaries, and scientists speculated that the whale swam away from the ocean in search of food either last fall or sometime this spring.

The whale carcass appeared to be in advanced stages of decomposition, but when scientists cut into it, they found the internal organs generally well preserved, according to Tom Seaton, a state biologist. The discovery indicated the 8-foot-long whale had frozen.

A fall trip would make sense, he said. The beluga likely followed migrating salmon up river.

But exactly what the whale was doing so far inland on a freshwater river is something "we'll never know for sure," he said.