The California Department of Fish and Game said Friday that "Olive the Oiled Otter" was spotted recently swimming on her back with a pup resting on her belly.
"Olive is an attentive mother, frequently grooming, nursing and holding her pup," the agency said in a statement.
The birth continued the remarkable story of the animal rescued in 2009 from a beach near Santa Cruz. It also was welcome news following a recent state and federal study that found tepid growth of the threatened California sea otter population on the Central Coast.
Scientists say oil is especially harmful to the species that has the thickest coat of any mammal. When the animal's coat is damaged by oil, its skin is exposed to cold water, which can lead to hypothermia and death because otters don't have a layer of blubber like other marine mammals.
The U.S. Geological Survey said there are 2,792 sea otters left in the California population, which spans more than 200 miles of the Central Coast, from Morro Bay to Half Moon Bay.
The animals once ranged from Mexico to Alaska, but they were hunted to near extinction in the early 20th century for their fur.
David Jessup, a veterinarian with the state wildlife agency who washed Olive, said the animal was "circling the drain" when she arrived.
"She was in very bad condition," Jessup said. "She had probably been oiled for some period of time and (had) not eaten."
For the previous two years, he had been researching techniques for washing oil off otters - the Monterey coast sees regular natural seepage, which likely was the source of Olive's oil.
Jessup and others bathed the otter in olive oil - hence the name - which he'd found could loosen the tar-like oil off the thick fur. Once cleaned, Olive was fed by Jessup and his staff.
After she recovered, Olive was outfitted with a microchip and transmitter and released back into the wild, where scientists have tracked and studied her.
Veterinarians understand the immediate health effects of oil on wildlife, but little is known about long-term impacts.
That makes Olive and her baby especially interesting to marine biologists.
"Few animals are available for long-term follow-up," said Bill Van Bonn, a veterinarian at the Marine Mammal Center in Sausalito, which rescues and rehabilitates marine mammals. "It illustrates the value of rehabilitation work."
Scientists discovered Olive was pregnant when she was brought in for a checkup and new transmitter in early August. Afterward, she moved from a Capitola surf spot she had been frequenting in recent months and became hard to find for a few weeks.
On Sept. 7, her transmitter beacon showed she had returned to her regular spot amid the kelp and surfers. When scientists went to check on her, Olive was floating on her back, cuddling her pup.
Since her release, Olive has gained a Facebook following, with hundreds of people offering congratulatory comments to the new mom.