RIO VISTA, Calif. (AP) – Two wounded, lost whales circled near a Sacramento River bridge Wednesday as boat crews prepared to bang metal pipes to try to herd them toward the open waters of the Pacific Ocean.

As the whales circled near the bridge, about 70 miles from the Pacific, scientists worried about their health, particularly the cuts apparently caused by a boat propeller. The Sacramento River water could hamper their recovery.

“The wounds appear to have worsened over time and their skin has changed from smooth and shiny to irregular and pitted,” said Frances Guiland of the Marine Mammal Center.

Skin samples taken from the mother whale on Monday were sent to labs to assess her general health and help identify her population stock.

Some crews in the more than two dozen boats blocking the humpbacks’ path up the river tried Tuesday to herd the mother and her calf downstream by banging metal pipes beneath the water. They planned to try again on Wednesday.

The scientists hope to encourage the pair to return to salt water quickly, without upsetting the whales.

“Stressing even a healthy whale is not good. Stressing an injured whale is worse,” said Brian Gorman, a spokesman for the National Oceanic and Atmospheric Administration.

The humpbacks, nicknamed Delta and Dawn, had traveled 90 miles inland more than a week ago, then turned around at the Port of Sacramento on Sunday and headed back toward the ocean. They were making progress until they reached the Rio Vista Bridge and began swimming in circles.

Scientists theorized the whales where upset by vibrations from traffic on the bridge.