Experts at the Whale Museum on San Juan Island have been monitoring the 20-year-old whale, known as J35, since her calf died shortly after birth last Tuesday.
For days now, the whale has been balancing the dead calf on her forehead or pushing it to the surface of the water.
Jenny Atkinson, the museum’s executive director, said the orca was still carrying her dead calf on Monday afternoon.
Ms Atkinson says the orca and her pod are going through “a deep grieving process”.
The calf was the first in three years to be born to the dwindling population of endangered southern resident killer whales. There are only 75 of the mammals left.