(AP) -- Biologists say they're concerned about the health of a gray whale that's stranded in the Klamath River in Northern California after swimming up with her calf a month ago.
The 45-foot mother and her 15-foot calf entered the Klamath in late June on their northward journey from their Baja California breeding grounds. They should be feeding in Alaska by now but instead took a detour in the river basin and went three miles inland, scientists said.
The unexpected visit created whale-watching opportunities for motorists on the Highway 101 bridge, where the whales cruised back and forth, but concern grew after several weeks that the mother wasn't getting enough food in the fresh water.
A team with the National Oceanic and Atmospheric Association and the Yurok Tribe, which owns the section of river where the whales have been lingering, filled power boats and kayaks over the weekend in an effort to drive them downstream with noise from banging pipes.
The team spotted an animal believed to be the calf swimming out to the ocean at the mouth of the river Saturday, but the mother remained upstream Monday.
Biologists believe the baby can survive in the ocean on its own because calves are weaning off their mothers at this point in the season, said Sarah Wilkin, the NOAA's stranding coordinator.
"If the calf weaned, all it needs to know is how to feed," Wilkin said. "Its chances of survival in the ocean are much better than in the river."
Meanwhile, the mother has refused to leave the waterway. In addition to food shortages, biologists are worried that the whale could become trapped in shallow waters or distressed by the influx of boats in the water as fishing season begins. The animal's skin condition also will deteriorate in the fresh water of the river.
"But the way she's looking right now, we think she's OK, at least for a little bit," Wilkins said.
The whale remained under observation Monday as biologists prepared for another trip into the river Tuesday to play acoustic signals, such as killer whale noises, that they hope will push her downstream, said Monica DeAngelis, an NOAA marine mammal biologist.
The last time whales were found stranded in California's coastal waterways for such an extended period of time was in 2007, when a pair of humpbacks - also a mother and calf - swam 90 miles up the Sacramento River. The whales stayed in the waterway for more than two weeks, drawing media attention and prompting a massive rescue effort, before quietly slipping back into the Pacific Ocean.
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