RIO VISTA, Calif. — The Sacramento River's humpback whale swam into a dead-end slough Saturday, scraping its belly on the bottom as it maneuvered through water less than 10 feet deep.
Surprising marine biologists who have watched the rare whale for more than a week, the 40-foot-long mammal managed to turn itself around in the channel, which is scarcely 40 feet wide.
By late afternoon, the 40-ton whale had moved down the slough into slightly deeper water but balked at swimming back under a small bridge it had crossed on the way upstream.
The gap between bridge pilings is about 10 feet, just large enough for the whale to squeeze through, said Bob Jones, a special agent with the National Marine Fisheries Service who flew over the scene in a helicopter.
Go Through or He's Stuck
"He's shown a reluctance to go back through," Jones said. "If he doesn't go through it, he's stuck up the slough."
Late Saturday afternoon, the whale swam in circles in the slough and exhibited signs of anger, including swishing his tail and blowing bubbles, according to Peter Chorney, a Fisheries Service agent.
The humpback whale swam into San Francisco Bay 10 days ago and began swimming up the Sacramento River. Since last Tuesday, it has been swimming near Rio Vista, drawing hundreds of whale watchers each day to this little delta town.
The crowds were disappointed on Saturday, when the whale seemed to have vanished. The only whale visitors saw was printed on T-shirts hawked along the roadside.
The Marine Fisheries Service, the Coast Guard, the Sacramento County and Solano County sheriffs' departments and the marine biologists searched for the whale by boat and airplane into the afternoon.
They finally tracked it down after a farmer reported seeing the giant creature up Shag Slough, about 25 miles south of Sacramento.
At one point, the searchers feared that the whale had become stranded and would die in the narrow channel, which is about 60 miles from the Pacific Ocean.
The water is so shallow that the animal's back was jutting into the air, and at times the whale seemed to wiggle along the bottom of the slough.
"He went up to the point of the slough where he couldn't go any farther," Jones said.
At that point the whale turned around and headed down the slough toward the main channel.
As night fell, the major obstacle to the whale's survival was the bridge--as much a barrier to his southward progress as the Rio Vista drawback had been earlier in the week.
From Tuesday to Friday, the whale swam off the town of Rio Vista, 10 miles to the south of Shag Slough. It stopped repeatedly north of the Rio Vista drawbridge, which is many times larger than the bridge the whale now confronts.
The U.S. Coast Guard closed the slough to all private boats in the hope that the whale, if left to its own devices, would go back under the bridge.