The saga of the two humpback whales that are stranded in a California river continued, unfortunately, on Tuesday. Scientists are concerned for the health of the two whales because they stopped in their journey back to the ocean habitat. The mother and calf circled for a second day at a bridge 120 kilometres from their natural ocean habitat.

According to the marine biologists on Tuesday the whales showed the first real signs of stress, rolling quickly from side to side in what observers described as a thrashing movement.

"We are concerned that she is getting increasingly stressed," said Frances Gulland, a veterinarian with the Marine Mammal Centre, who was aboard a boat tracking the whales, dubbed Delta and Dawn. Also Gulland warned that there have been changes for the worse in the whales' propeller wounds and skin condition.

On Sunday, marine biologists manages to make the whales to swim from from the Sacramento Port back to ocean, after previously they resisted scientists' attempts to lure them using recordings of whale feeding calls.

On Monday, the reports were positive as the whales had swum some 40 kilometres to Rio Vista, where they stopped just before a bridge. In the next day, scientists