Heidi Perryman, the founder of the local beaver advocacy group Worth a Dam, said the group got a report about a month ago that a baby beaver had been spotted.
The group had been keeping an eye on the creek since then to confirm the report, and on Sunday, the beaver kit was spotted again.
"It was out again last night, and it's been out again every night this week," Perryman said.
She said the new kit brings the family total to at least five beavers, and that it's possible there are other kits that haven't yet been seen.
The whole family is helping take care of the young creature, which she estimates is about six weeks old.
"I've never seen so many adult beavers fussing over a kit," she said.
Perryman invited residents to check out Worth a Dam's fifth annual Beaver Festival in downtown Martinez on Aug. 4.