Corpses of five harbor seals were discovered together in Bolinas Lagoon this week, as a mysterious, month-long epidemic continues to plague the West Marin coast.

Within the last two weeks, 11 adult harbor seals have washed up on stretches of beach near Double Point, on Bolinas Beach, and along Ten Mile Beach. None of the seals had visible injuries.

"There's no evident signs of any kind of disease," said Margaret Burks, executive director of the Marine Mammal Center. "They are just washing up, apparently healthy but dead."

Because most of the corpses have been too decomposed to yield useful information, full necropsies have been performed on only four of the seals. The necropsies revealed white nodules in the seals' lungs, suggesting they suffered from an infectious disease.

"It has the indication it might be viral," said Dr. Sarah Allen, an ecologist at the Point Reyes National Seashore. She said researchers are analyzing tissue samples at UC Davis Veterinary School to determine a specific cause of death. The results are expected within a month.

Because the local population of harbor seals is estimated to include over 5,000 adults and pups, scientists aren't too alarmed over the deaths, but Burks warned the epidemic may be affecting seals throughout the region.

"It's really hard to tell," she said. "Because the North Coast is so rugged, they could have died and not been discovered yet, or they could have been eaten."

Allen said a couple of adult corpses are usually discovered during breeding season, from March to June, when diseases most easily spread through the population as they congregate.

"You don't find dead adults very often, or even sick ones," she said, citing two notable exceptions: An undiagnosed viral infection that spread through the local population in 1986 and a European epidemic of canine distemper that killed about 4,000 seals, also in the 1980s.

Allen said it is vital for beachgoers to report dead seals immediately to the Park Service or to call the Marine Mammal Stranding Network, 750-7177. Live stranded seals should be reported to Marine Mammal Center, 289-7325.

Both Burks and Allen noted that it is a violation of federal law to disturb any Marine Mammal, dead or alive.