Humpback whale spotted in Sacramento River near Rio Vista

An unexpected visitor has made its way into the Sacramento River, with an adult humpback whale traveling deep into the Sacramento-San Joaquin Delta.

The whale, identified as CRC-11620, was spotted near Rio Vista after first entering San Francisco Bay earlier this week, according to the Marine Mammal Center.

The center said its Cetacean Conservation Biology Team is tracking the whale and coordinating with partners as more information becomes available.

The whale was first reported in San Francisco Bay on Sept. 15, then later traveling north past the Richmond-San Rafael Bridge. From there, officials said it continued east into the Carquinez Strait near Benicia and Dillon Point.

By the morning of Sept. 16, the U.S. Coast Guard reported the humpback farther up the Delta near Collinsville and Sherman Island.

The latest reports placed the whale in the Rio Vista area, where its appearance has drawn attention because of how far inland it has traveled.

"This is a remarkable journey for a humpback whale," said Kathi George, director of Cetacean Conservation Biology at The Marine Mammal Center. "We're asking people who encounter it to give the animal plenty of space and allow it to move on its own."

A familiar but unusual journey

While a humpback whale traveling this far into the Delta is unusual, it has happened before.

In 1985, a whale known as Humphrey spent several weeks in the Rio Vista area before eventually returning through San Francisco Bay to the ocean.

In 2007, a mother-and-calf pair known as Delta and Dawn spent about 20 days in the Sacramento River Delta before making a similar trek back to the ocean.

Multiple humpback whales have also been sighted in San Francisco Bay over the past week, which the center said is normal for this time of year.

Whale identified through photo catalog

The Marine Mammal Center said CRC-11620 is a well-known individual that has been documented more than a dozen times over the past 24 years in California and Mexico.

Its first recorded sighting off California was in 2002. Before this week, CRC-11620 was recorded in Baja California in February 2026.

The Marine Mammal Center said it is not known whether the whale is simply passing through the Delta or whether an underlying health issue could be influencing its movements.