The two whales, which were lost in the Sacramento rivers are finally moving back to ocean after two weeks. The whales, a mother and her calf, nick-named by marine biologists, Delta and Dawn, are 55 kilometers far from the ocean.

The pair begins their trip back to Pacific last week, but shortly after theu stopped 120 kilometers from the ocean, at the Rio Vista bridge.

Since the whales had swim up the river, the marine biologists had tried different methods in order to lure them back to the ocean.

Bernadette Fees, a biologist with the California Department of Fish and Game, said in broadcast remarks that she would be administering antibiotics - one dose for the calf and three doses for the mother - to help them deal with skin infections that apparently resulted from cuts delivered by passing boats. She also said she would work to take a biopsy from the calf.

But a new problem has emerged as the whales swim down the river. As they are getting closer to the San Francisco Bay, the humpback whales may encounter large oceangoing vessels that could harm them.

"These larger vessels are a real concern to us," said Greg Hurner, a senior adviser with the California Department of Fish and Game. "We will try to keep a safe zone around them, and our enforcement vessels will reach (larger boats) on the marine channel."