Some crews on more than two dozen boats working to block the humpbacks’ path up the river have been trying since Monday to drive them downstream by banging metal pipes beneath the water. They 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 before turning around at the Port of Sacramento on Sunday and heading back toward the ocean. 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. RIO VISTA – Scientists worried about the health of two wounded, lost whales circling near a Sacramento River bridge planned to begin banging metal pipes again today to herd them toward the open waters of the Pacific Ocean. The humpback whales, who wandered up the river more than a week ago, were spotted again this morning near the bridge about 70 miles from the Pacific where they have lingered since Monday. Both whales were apparently wounded during a run-in with a boat’s propeller. “The wounds appear to have worsened over time and their skin has changed from smooth and shiny to irregular and pitted,” said Frances Gulland of the Marine Mammal Center. Fresh water could hamper the humpbacks’ recovery, adding urgency to scientists’ efforts to push the mother and her calf back to their saltwater home, biologists said. 160Want local news?Sign up for the Localist and stay informed Something went wrong. Please try again.subscribeCongratulations! You’re all set!