A third killer whale that swam up the Nushagak River has been found dead.

A spokeswoman for NOAA's National Marine Fisheries Service said the carcass of the third whale, a juvenile, was spotted Friday near Grass Island, across the river from Dillingham in an area influenced by tides.

Julie Speegle said in a statement that biologists believe the juvenile likely swam there rather than floating on the tides.

The juvenile and two female orcas, including one pregnant whale, were spotted in fresh water more than three weeks ago. Necropsies last week on the other two whales provided no obvious reasons for why they died.

Speegle said nothing has been decided regarding a necropsy or tissue samples from the juvenile carcass.