Humpback Whale Swims 60 Miles Inland Into California River
A group of friends went fishing on California’s Sacramento River last week and ended up spotting something much bigger than they expected. A humpback whale surfaced near their boat about 60 miles from the Pacific Ocean.
Denny Glover was fishing for salmon and striped bass with friends near Rio Vista on Sept. 16 when one of them said he saw a whale. At first, Glover didn’t believe him and thought he might have seen a dolphin or porpoise instead.
Then the whale came back up. Glover was able to record several videos as the adult humpback surfaced in the river before disappearing underwater again.
The whale had already been making its way inland by that point. The Marine Mammal Center says it was first reported in San Francisco Bay on Sept. 15 and then continued into the Sacramento-San Joaquin Delta near Rio Vista.
Researchers Know This Whale
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Researchers were able to figure out exactly which whale had made the unusual trip. It is known as Rio, or CRC-11620, and they have been keeping track of it for more than two decades.
Rio has been documented 15 times over the past 24 years in California and Mexico. The first recorded sighting was off California in 2002, while the most recent one before this trip was in Baja California in February 2026. Researchers don’t know if Rio is male or female.
The Marine Mammal Center says the U.S. Coast Guard reported the whale even farther up the Delta on the morning of Sept. 16. The center is working with other groups to keep an eye on Rio and see how the whale is doing.
For now, there isn’t an answer for why Rio went so far inland. The center says the whale could simply be passing through, but it also hasn’t ruled out an unknown health problem.
This Has Happened Before
Rio isn’t the first humpback to end up around this part of California. A humpback named Humphrey spent several weeks around Rio Vista in 1985 before eventually making it back through San Francisco Bay and into the ocean.
Then, in 2007, a mother and calf known as Delta and Dawn spent about 20 days in the Sacramento River Delta. They also eventually headed back toward the Bay and the ocean. The Marine Mammal Center was involved in both of those cases.
Researchers are asking you to Give Rio Plenty of Space
People hoping to see Rio are being asked not to get too close or try to steer the whale back toward the ocean. The Marine Mammal Center says boaters, kayakers, paddleboarders and anyone else on the water should stay at least 100 yards away.
NOAA gives the same general recommendation for large whales. It also advises boats not to chase, surround or cut in front of them.
“This whale is in an out-of-normal habitat area,” Kathi George, the Marine Mammal Center’s director of Cetacean Conservation Biology, said. “Our team is actively monitoring the situation, and we kindly ask the public to please avoid changing the whale’s course and let the animal decide where it wants to go.”
