The marine scientists had managed to lure back to the sea the two humpback whales. The whales, a mother and her calf, were spotted last Sunday in the lower Sacramento River. They had swimming more than 160 kilometers up the Sacramento River, but this Sunday wildlife authorities and scientists drove them back to the Pacific Ocean.

Wildlife authorities believe that the mammals had taken the wrong turn during their annual migration from Baja Mexico to their summer feeding grounds in Alaska. Both whales are injured, but the wounds are not considered life- threatening by the scientists. Even they are heading to the Pacific Ocean, there are a lost obstacles in front of the whales.

"The really worrisome thing is down the Delta," said Brian Gorman, a spokesman for the National Oceanic and Atmospheric Administration. "There are all sorts of diversions and all sorts of wrong turns."

In order to keep the whales on track officials set up other vessels to block entrances to other tributaries on the Sacramento Delta.

"We don't know why they came up the river, or why they are moving down," said Bernadette Fees, a spokeswoman for the California Department of Fish and Game. "As you can see, they are making their own decisions, and we are just trying to keep up with them."