By admin 
The Sacramento Delta recently had a surprise visitor.
On Sept. 16, fishermen spotted an adult humpback whale in the waters near the Rio Vista Bridge.
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The Marine Mammal Center in Marin later identified the whale as CRC-11620, who has been spotted up and down the California coast more than a dozen times in the past 24 years.
Humpback whales tend to keep to the open sea, but the massive marine mammals occasionally venture into the fresh waters of the Sacramento River.
Humphrey the humpback whale famously swam within 33 miles of downtown Sacramento in 1985, and his journey into the Delta ended in a high-profile rescue. More recently, a mother humpback and her calf swam into the Delta in 2007.
Here’s what you should know about our wild visitors:
What happened to humpback whale seen in Sacramento River?
After spending several days in the Delta, CRC-11620, nicknamed “Rio,” was last seen on Sept. 21 near Port Chicago, according to the Marine Mammal Center.
The whale was moving west in the direction of the San Francisco Bay.
“We haven’t had any follow-up reports,” said Giancarlo Rulli, spokesperson for the Marine Mammal Center. “The fact that there have been none leads us to believe that Rio exited out.”
If you see something large moving in the waters of the Sacramento River, it’s likely another marine mammal entirely.
“The calls that we’ve been receiving have all been about sea lions,” Rulli said.
How common are sea lions in the Sacramento River?
California sea lions swim into the Delta from the ocean seeking fish, Rulli said.
Many of the sea lions seen in the area are males returning from their breeding grounds on the Channel Islands, and “bulking back up after a long migration,” Rulli said.
Sometimes, sea lions can be spotted from the banks of the Old Sacramento district, swimming or sunning themselves
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What should I do if I see a California sea lion?
The Marine Mammal Center cautions against getting too close to sea lions and whales, for everyone’s safety.
Boaters, paddleboarders and swimmers should all keep their distance.
California sea lions can weigh 600 to 800 pounds.
Sea lions can be aggressive when they are carelessly approached, and they are illegal to hunt or harass under the Marine Mammal Protection Act.
Humpback whales can weigh up to 40 tons, or, 80,000 pounds.
“Give them a wide berth,” Rucci said.
How can I tell if there’s a whale in the water?
Sometimes, “we get reports back of a whale, and it’s actually a large California sea lion that’s surfacing and then diving,” Rulli said.
Other marine mammals, such as harbor seals, have also been known to swim into the Delta.
Dolphins and harbor porpoises also swim into the area from time to time, though it’s extremely rare.
According to Rulli, here are some simple ways to tell if you’re actually seeing a whale:
- As opposed to a sea lion, “there would be a much larger water dispersal” with a whale, Rucci said.
- When whales exhale, it creates a smoke-like “spout” in the air. “As spouts tend to linger for a moment above the ocean surface, they are a telltale way to know that a whale is nearby,” the Marine Mammal Center said.
- When whales dive, their backs form a curved arch above the water. This cause humpback whales to display the humps on their dorsal fins.
What should I do if I spot a whale?
If you end up seeing a whale in the waters of the Delta, you can report it to the Marine Mammal Center at its website or the WhaleAlert app.
According to guidelines from the National Oceanic and Atmospheric Administration, it is safest to stay at least 300 feet away from whales and 150 feet away from sea lions.
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This story was originally published October 15, 2026 at 9:00 AM.