Meanwhile, wildlife officials will be working on plans to evaluate the health of the mammals and come up with a plan to lure them back down the deepwater shipping channel, to San Francisco Bay and eventually the ocean.
The whales -- believed to be a mother and calf -- were first seen on Mother's Day in the Delta and again on Monday near Rio Vista. The animals have since swam up the Sacramento River and into the deepwater channel that leads to the port.
Biologists said they are not sure why the whales have found their way nearly 80 miles inland from the Golden Gate.
But Francis Gulland of the Marine Mammal Center said the whales may have been driven farther inland by people in boats and on shore trying to spot them. Authorities are uging the public to stay away from the whales.