Rio Vista, Calif. ? Hope dimmed Wednesday for two lost, wounded whales as scientists spotted the humpbacks wildly slapping their tails on the water in possible distress as they lingered far from their ocean home.

A group of boats gathers on the Sacramento River near Rio Vista, Calif., as crew members attempt to drive two humpback whales down the river by banging on metal pipes extended into the water. The mother whale and calf showed growing signs of distress Wednesday, and made no progress toward returning to the ocean.

Deep cuts on the mother whale and her calf, likely caused by a run-in with a boat, were worsening after more than a week in freshwater surroundings that the pair were not physically well-equipped to inhabit, biologists said.

“I wouldn’t say there’s a lot of optimism right now,” said Brian Gorman, a spokesman for the National Oceanic and Atmospheric Administration.

“They may surprise us again. They may just take off and head down river. But as long as they continue doing what they’re doing, we’re very worried about them.”

For a third day Wednesday, the pair – nicknamed Delta and Dawn – frustrated efforts to herd them past a Sacramento River bridge, where they have lingered about 70 miles from the Pacific.

Boat crews who were banging on metal pipes beneath the water to urge the whales downstream called off the effort temporarily Wednesday, with scientists saying they needed to rethink their strategy.

“We’ve done the best we can with the piping, so now we have to look at something else,” said Carrie Wilson, a marine biologist with the California Department of Fish and Game.

Scientists said they were concerned about the tail-slapping behavior, known as “lobbing,” because the whales had been swimming along calmly since they wandered upriver more than a week ago.

“The whales were fairly quiet for a period of days. Then they weren’t so quiet. So the question is, why have they changed?” said Trevor Spradlin, a NOAA whale biologist.

But the biggest worry was the wounds on both whales, especially a 3- to 4-foot cut down the side of the calf that appeared to pierce the blubber layer down to the muscle.

The freshwater environment was putting a physical strain on the whales, turning their skin from its normally smooth, shiny texture to rough and pitted, “like when you sit in a bathtub for too long,” Spradlin said.

The stress of that continued exposure “may be impeding their natural healing abilities,” he said.

Scientists initially believed that the humpbacks had been wounded by a boat’s propeller. But a comparison of injuries with photographs of other wounded whales suggested the pair had been more likely sliced by a boat’s keel or skeg, a fin jutting below a boat’s outboard motor, Gorman said.

The humpbacks apparently took a wrong turn during their annual migration to feeding grounds in the northern Pacific. They were making progress Monday until they reached the Rio Vista Bridge and began swimming in circles.

Scientists theorized the whales began circling because vibrations from traffic on the bridge upset them, though the pair continued to circle even when traffic was halted.