First spotted by the U.S. Coast Guard's Rio Vista station Sunday, the mother and calf subsequently swam up the Sacramento River until they reached a dead end in the turning basin of the Port of Sacramento.
Marine experts spent three hours Wednesday examining the mammals as hundreds of bystanders flocked to a nearby levee hoping to glimpse the first whales to show up at the port since it was built in 1963.
Their appearance so far from home has touched off a media frenzy that took Port Director Mike Luken aback as reporters from across the Bay Area descended on the port for an afternoon news conference.
"I've never seen anything like this," Luken said as a few yards away a sleek black mass momentarily broke the surface of the water only to disappear just as quickly.
Frances Gulland, a veterinarian with the nonprofit Marine Mammal Center in Sausalito, said at the news conference that both mammals had wounds that at this point didn't appear to be life-threatening.
The approximately 45-foot female and her 20-foot calf probably were struck by a medium-size boat propeller several days ago during their journey into the Delta, she said.
The adult has a gash about 2 feet long and 6 inches deep in front of the dorsal fin, said Gulland, who considers the wound superficial.
The calf appears to have suffered more serious injuries on its right side just below the dorsal fin, but Gulland said she could not elaborate because it had come out of the water far enough for her to get a look only twice.
She said that there is no need to treat either mammal as long as rescuers soon can get the pair back to salt water, where the wounds would heal more quickly.
Prolonged exposure to fresh water could cause their skin to blister and peel, Gulland added.
Humphrey, a humpback whale that wandered the Delta for 26 days in 1985, developed these symptoms during the final week, she said, although he did not suffer any permanent damage.
Contrary to earlier reports, neither whale was entangled in any netting, Gulland said, adding that she and others will examine photos taken Wednesday morning for more information.
Starting midmorning today, authorities plan to launch a twofold rescue operation that will start by piping underwater the sounds that humpback whales make when they're feeding to entice the creatures out to San Francisco Bay.
If they can get them moving, Gulland said, a flotilla will follow the pair to discourage them from reversing course.
The state Department of Fish and Game's law enforcement division has several boats at the ready, and those will join about a half-dozen more that will be waiting around Rio Vista where the river widens, said Lt. John Laughlin.
Also on scene will be officials from the Long Beach offices of the National Marine Fisheries Service, which is overseeing the rescue.
Personnel from U.S. Coast Guard Sector will be on hand to help keep other boats at least 100 yards from the whales, and they are asking pilots to maintain an altitude of 1,000 feet or more.
Federal law prohibits the public from harassing the creatures by doing anything that causes them to deviate from their normal behavior.
Humpbacks are an endangered species with numbers around 6,000 in the waters off the West Coast, according to the latest stock report from the federal agency that oversees National Marine Fisheries Services.
Gulland was not predicting how long it would take to herd the whales back to the Pacific Ocean, noting only that Humphrey made it back to salt water in two days once he got back on track.
"I'd love this (the rescue) to be over in a week," she said.
The whales have not been feeding since arriving in the Delta because it does not contain the sardines and anchovies they typically eat, Gulland said. The female's fat reserves are at their lowest right now because she just completed her migration north and humpbacks don't eat during their approximately six-month breeding season in the warmer waters of Mexico and Costa Rica, she added.
Among the curious who turned out to see the whales was David Anderson, a West Sacramento resident who spent about a half-hour admiring the giants despite their low profile.
"It's nothing spectacular," he said. "You see a little bit of their nose. I'd actually like to see them come out of the water, but they're not here to entertain me."
Anderson was among many who received a traffic citation for trying to park within walking distance of the port, but he shrugged off the annoyance.
"It's the price of admission," he said.
Reach Rowena Coetsee at 925-779-7141 or firstname.lastname@example.org.