California ? Two whales lost in the Sacramento River encouraged biologists Monday by making progress toward their ocean home, but then abruptly halted their journey at a busy bridge.

Unlike the relatively narrow section of the river where the two had lingered for the past week, the whales were in a holding pattern in a much wider waterway teeming with traffic.

“Right now they are meandering, but we’re hoping that they get it in their minds to keep going,” said Rod McInnis, a spokesman for the National Oceanic and Atmospheric Administration.

The shift came after an encouraging spurt in which the pair traveled about 24 miles in 24 hours. They were first spotted May 13 and got as far as 90 miles inland to the Port of Sacramento before turning around.

The mother humpback whale and her calf were seen Monday morning near the Benicia-Martinez Bridge, about 45 miles from the Pacific, said Carol Singleton of the Governor’s Office of Emergency Services.