The Marine Mammal Center has been tracking reports of a humpback whale that entered San Francisco Bay this week and continued traveling east into the Sacramento-San Joaquin Delta near Rio Vista.
First reported in the bay on Tuesday, the adult whale has been spotted near the Richmond ship channel, traveling north past the Richmond-San Rafael Bridge, before being sighted farther east in the Carquinez Strait near Benicia, according to the Marine Mammal Center.
By Wednesday morning, the U.S. Coast Guard had reported a humpback whale farther up the Delta.
As of Thursday evening, there have been no other sightings, the Marine Mammal Center said.
“While it’s unknown whether this whale is just passing through or if there is an underlying, unknown ailment, the best thing people can do is experience this adult whale’s presence from a respectful distance,” said Kathi George, director of Cetacean Conservation Biology at the Marine Mammal Center.
The individual whale, known to researchers as CRC-11620, has been documented 15 times over the past 24 years in California and Mexico, with its first recorded sighting occurring off California in 2002, according to the Marine Mammal Center.
The most recent sighting before this week was off Baja California in February 2026. It’s not known if the whale is female or male. The whale’s route can be tracked through Happywhale.
There have been multiple humpback whales spotted in San Francisco Bay over the past week, which is normal for this time of year.
It’s not the first time a humpback whale has made the journey into the Delta. In 1985, the whale known as Humphrey spent several weeks in the Rio Vista area before returning through the bay to the ocean. In 2007, a mother-calf pair known as Delta and Dawn spent approximately 20 days in the Sacramento River Delta before eventually making their way back toward the bay and ocean.
While giving it ample space, anyone who sees the whale is asked to help experts by reporting sightings on the Marine Mammal Center website or via the WhaleAlert app.
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