Unfazed by the sounds of other whales and clanging pipes, two wayward humpback whales will next encounter the spray of fire hoses, which scientists hope will herd them back toward the ocean.

The two whales, a mother and her calf, remained in the Sacramento River, some 70 miles from the Pacific, where they've been circling for days.

On Friday, biologists planned to spray water near the whales from above and underwater from the deck of a boat on the river.

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"No one has done this before," said Frances Gulland, who is leading the campaign to move the pair back to the ocean. "At this point, we don't know if it will be a deterrent or an attractant."

The humpbacks apparently took a wrong turn during their annual migration to feeding grounds in the northern Pacific. They traveled 90 miles inland to the Port of Sacramento before turning around.

They were making progress Monday until they reached the Rio Vista Bridge and began swimming in circles.

Officials gave the pair a break from relocation efforts Thursday. The physical condition of the whales had not changed much, but their wounds — apparently caused by a collision with a boat's propeller — continued to deteriorate.

"We don't want to do anything that will impose stress on them today," said Carrie Wilson, a biologist with the state Department of Fish and Game. "We do not want them to become habituated or desensitized to the different types of things we're doing to coax them down the river."

The rescuers also are working on a plan to inject the whales with antibiotics to help their wounds heal. Scientists are still developing the drug and will likely use a syringe attached to a pole or a dartgun to administer it, said Gulland, director of veterinary science at the Marine Mammal Center in Sausalito.

Rescuers said Thursday they planned to continue efforts to move the stranded whales over Memorial Day weekend if the animals had not started moving on their own.

U.S. Coast Guard crews would keep a 500-yard buffer zone around the whales to keep boats away. They expected crowds of whale watchers to gather along the riverbanks to catch a glimpse of the humpbacks.