A female gray whale remains stuck in a Northern California river despite scientists' efforts to nudge the 40-ton mammal seaward with unpleasant underwater sounds.

Sarah Wilkin of the National Oceanic and Atmospheric Association says a rescue team Tuesday played killer whale and alarm sounds through speakers mounted on a boat on the Klamath River.

The team had hoped the sounds would help send the whale back in the direction of the Pacific Ocean a few miles (kilometes) downstream, but to no avail. The mother and her calf wandered into the river in late June.

Wilkin says the calf apparently weaned itself from the mother and returned to the ocean late Saturday.

Scientists are concerned the mother will not find enough food and that her skin will suffer in the freshwater environment.