A humpback whale was spotted in a California river, 60 miles from its Pacific Ocean home

ALAMEDA, Calif. (AP) — Denny Glover was hoping for a big catch when he went fishing with buddies on the Sacramento River, but he wasn’t expecting a fully grown humpback whale.

Glover saw the whale surfacing on Wednesday while he was fishing for salmon and striped bass from a 21-foot (6.4-meter) boat, less than half the length of the animal. He shot a few videos as the whale broke the surface of the water in California’s largest river, about 60 miles (97 kilometers) from its more typical home of the Pacific Ocean.

“One of the guys on the boat, he said, ‘I see a whale.’ He saw the spout,” Glover said. “At first we didn’t believe it. We thought he had mistaken a dolphin or a porpoise. Then we saw the spout again, and there’s no mistaking a whale spout.”

The rare inland visit from a whale has attracted the attention of scientists who want to know what kind of condition it’s in and how it wound up so far from the sea. The whale entered San Francisco Bay earlier in the week and has been traveling east in the Sacramento-San Joaquin Delta, California’s largest river delta, The Marine Mammal Center said in a statement.

The center, which is in Sausalito, said its cetacean team is planning to assess and monitor the animal. The public should avoid interacting with the whale and trying to change its course, said Kathi George, the center’s director of cetacean conservation biology.

“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,” George said.

The whale is known to researchers through a photo identification catalog and has been documented 15 times over the past 24 years, the center said. The most recent documented sighting before this week was in Baja California in February, the center said. Researchers don’t know whether the whale is male or female.

The California Department of Fish and Wildlife and National Oceanic and Atmospheric Administration both declined to comment about this week’s sighting.

The whale isn’t the first to travel so far inland. In 1985, a humpback whale known as Humphrey spent several weeks in the Rio Vista area before returning to the ocean, The Marine Mammal Center said. A mother-calf pair known as Delta and Dawn spent nearly three weeks in the Sacramento River Delta in 2007 before returning, the center said. The whales eventually made their way back to the ocean, the center said.

Humpback whales are among the largest animals on Earth and can weigh up to 80,000 pounds (35,287 kilograms). They are known for their dramatic lunges at the water’s surface, an activity called breaching, and their complex underwater songs.

Seeing the whale so far upriver was a thrill, Glover said. The animal seemed in good shape despite being far from home, he added.

“It came up and went down in fairly regular intervals,” he said. “It was moving along at a fair clip. It wasn’t acting erratically other than that it was upstream in a freshwater river.”

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Whittle reported from Portland, Maine.