Here's the latest from the scene:
4:45 p.m.: Mother whale shows stress
A veterinarian who's been monitoring two humpback whales since they appeared in the Delta nine days ago reported Tuesday afternoon that they appear to be deteriorating.
Frances Gulland, a veterinarian with Marine Mammal Center in Sausalito, says she's seeing changes in the skin of the adult female and her calf.
The surface has gone from smooth and shiny to irregular and pitted, she said.
Gulland added that the gashes both whales have received -- probably from a ship's propeller -- seem to be getting worse.
Earlier she had noted that prolonged exposure to fresh water not only can interfere with healing but cause a whale's skin to blister and peel.
11:50 a.m. Rescuers must deal with wind
Strong winds and somewhat rough water conditions have challenged rescuers in their efforts to steer the wayward whale and her calf down river this morning.
The meandering mammals continue to swim north of the Rio Vista bridge this morning near Ryer Island as rescuers in boats tried to herd them back through the River Vista Bridge toward the sea. So far they've been under the bridge at least three times in the last day, but each time they've
The experts plan to keep up the pipe-banging methods today. They will also continue trying to attach a satellite monitoring tag to the mother, but that effort has proved tough with winds gusting at more than 20 miles an hour.
9:20 a.m. Rescue efforts resume
The whales were sighted from the air at about 8:30 a.m. this morning approximately three miles north of the Rio Vista Bridge, according to government officials on the week-long whale watch.
Rescue efforts were scheduled to resume at 9:30 a.m., at which point those aboard the 26 boats currently at the site will start hammering on 6-foot metal pipes to drive the pair down river, said a spokeswoman for the governor's Office of Emergency Services.
8:30 a.m. Flotilla awaits in Rio Vista
A CHP helicopter will soon begin an air search in the area of the Rio Vista Bridge and beyond in an effort to try to locate the two wayward whales.
Earlier this morning, a U.S. Coast Guard helicopter failed to locate the missing duo despite repeated sweeps of the area.
A flotilla of boats is in Rio Vista ready to begin rescue efforts as soon as the whales are spotted. Experts had hoped to attach a GPS-like satellite tracking device beneath the mother's fin so they could more easily locate the mammals, but strong winds made that impossible last night.
7 a.m. Metal pipe banging helped little
The whales were swimming in circles near the Rio Vista Bridge as their journey back to the Pacific Ocean stalled more than a week after they took a wrong turn and ended up in the Sacramento River.
"They're wild animals and they're going to do what they want," Coast Guard Petty Officer Brian Leshak said late Monday night.
The humpbacks, nicknamed Delta and Dawn, had traveled more than 20 miles south following their sudden departure from the Port of Sacramento on Sunday night. But then the mother and her calf then started swimming in circles near the Rio Vista Bridge.
Scientists and the U.S. Coast Guard had tried to position more than a dozen boats in front of them to turn them around, but the whales appeared to be navigating by their own compass.
Attempts to guide the whales toward the ocean by causing vibrations by banging metal pipes in the water did not work Monday.
"We're reassessing what to do and we're working on a plan to actually herd the whales," Leshak said.
Scientists continued to watch closely because their route includes sloughs leading to muddy deltas that could trap the whales, who appear to have been wounded by a boat's propeller. Crews were trying to position boats at the mouths of side channels to keep the whales from going off course.
The two also will have to make their way through the pylons of four bridges to reach the San Francisco Bay, and will have to swim under the Golden Gate Bridge to return to the ocean, Wilson said.
Federal officials have authorized researchers to fire darts carrying a satellite tracking device beneath the mother's fin to ensure authorities can still locate the whales if they wander from the river into the delta's maze of tributaries.
"They're at this point lost. We don't think they have any clue," Rod McInnis of the National Marine Fisheries Service.
The whales started moving toward the Pacific around 3:30 p.m. Sunday, swimming at about 6 mph, from the Port of Sacramento, where crowds had gathered over the weekend to catch a glimpse.
The pair journeyed as far as the Rio Vista Bridge in the rural Sacramento-San Joaquin River Delta region before turning around. Scientists theorized that vibrations from traffic were upsetting the mother and calf, but the whales could not be coaxed forward even when the drawbridge was raised to halt the flow of vehicles.
No one is certain why the whales decided to go back downstream in the first place, but Jim Oswald of the Marine Mammal Center said the change may have been spurred by tug boats. The tugs' engines fired up about 100 yards away from the pair, and the sound may have had an influence.
"The tugs were out in the basin and the whales decided to follow them," Oswald said.
Wilson said there was no indication that the whales were in poor health. "They have been very consistent, and moving along at a good pace," she said.
The whales' plight has been followed closely, with thousands of people gathering along the banks of the port and the river to see the pair.
The appearance of the humpbacks was not the first time a West Coast whale has veered so far off course during the annual spring migration northward. A humpback named Humphrey swam in the delta for nearly a month in 1985 before scientists used recordings of whale songs to lure him back to the Pacific.
Associated Press writer Aaron C. Davis in Rio Vista contributed to this report.