Although the Department of Fish and Wildlife said labs have narrowed down the possibilities of what the gooey substance could be, the source of the deadly pollution has not yet been located.
California Department of Fish and Wildlife researchers working in conjunction with two federal labs have determined the goo was made up a mixture of non-petroleum-based fats or oils.
When the fats or oils come into contact with the hair and feathers of wildlife they can cause similar effects as petroleum products including loss of thermal insulation and buoyancy.
"It sounds simple, but it's very complicated chemistry." Dave Crane, Environmental Program Manager at California Fish and Wildlife. "We may not know what we're looking for, but there are a lot of things to figure out that are easier than this has been."
Officials said secondary effects can include hypothermia, starvation, drowning, predation, entrapment, suffocation, opportunistic infections and death.
"This was like a giant jigsaw puzzle with thousands of pieces to put together," said Environmental Scientist Janna Rinderneck. "We had many possibilities of what this material could be. Working together, the laboratories have narrowed that list.
"On January 16, seabirds began turning up in the East Bay covered with this "mystery goo." International Bird Rescue workers took the lead in caring for 323 birds that were captured alive. An additional 170 birds were collected dead.
The number of impacted birds that may have sank, lost to predation or were missed during searches is unknown, officials said.
As the report was being released on Thursday, wildlife officials were returning six of the goo-covered birds back to the wild after they had been nursed back to health at the International Bird Rescue's Fairfield center. About 80 of the birds have now been returned to the wild.
"We're doing this all on our own there is no responsible party," said Russ Curtis of the International Bird Rescue. "We've incurred a big cost, but luckily the public stepped up and helped."
"He came in completely covered and couldn't flap his wings. Everything was stuck to him. He couldn't move." said International Bird Rescue volunteer Kathy Koehler, talking about a bird nicknamed "Gummy Bear" who was among those released Thursday.
Curtis said there was a great deal of joy when an injured bird can be returned to the wild.
"I would say a release of birds lifts your spirits," he told KTVU.
The investigation continues to identify the source of the contaminant. If you have any information on the incident, contact CalTIP at 1-888-334-2258.
International Bird Rescue has spent hundreds of thousands of dollars on clean-up and rehabilitation of birds since the problem first surfaced, according to Curtis.
"We'd love to send somebody a bill. And we'd also like to educate them to say, you know the San Francisco Bay is not a dumping ground. Birds live here. We live here. And we want it to be a safe spot for both of us," said Curtis.
For information on how to donate to help International Bird Rescue, visit the organization's website.