The dead birds are suddenly piling up. Normally, the Richardson Bay Audubon Center sees two or three per week.
Today alone, they collected 21 from around the Tiburon shoreline.
"Clearly something is still happening. Birds are dying really recently and we're picking them up on the beach," said Wildlife Sanctuary Kerry Wilcox.
The Wildlife Sanctuary reports finding about 70 dead birds since January 26; the day after the first of two major sewage spills.
The public didn't find out about that first spill until a few days ago. The second release happened last Thursday.
A total of five million gallons of wastewater went into Richardson Bay, but nobody is saying outright that the spills are to blame.
"To have so many at once wash up on shore like this, so soon after the sewage spill is a little suspect," said Wilcox.
"It's a very hard way to learn about birds. It's a very good way. Most of these birds we usually see far out at sea," said Brooke Langston from the Richardson Bay Audubon Center.
Brooke Langston, with the Richardson Bay Audubon Center says there's no obvious cause of death.
"We're not seeing anything on them that's telling us why they're dead, there is not oil. There's not trauma," said Langston.
One of the concerns is that whatever possibly killed the birds in Richardson Bay, may now be working its way into the animal food chance as birds and other creatures feed on the remains.
The San Francisco Bay Regional Water Board says bacteria levels are safe enough that the water is okay for recreational use. But residents still want answers about the dying birds.
"Well I'd like to know if it is because of the sewage or is there something perhaps more wrong," said Tiburon resident Leonora Balfour.
On Thursday, Sewerage Agency of Southern Marin announced it would hire an independent investigator to look into the spills.
The dead birds were taken away to be analyzed to determine what killed them, those results could take a few days.