An American amateur fisherman who was dragged overboard by a sea lion has revealed he feared for his life.

Accountant Dan Carlin, 62, was dragged 20 feet below the surface by a sea lion while posing for a photo on his boat in the San Diego bay.

Carlin was holding a yellowtail fish that he had caught earlier, which attracted the unwanted attention of the hungry sea lion.

The mammal leapt from the water and sunk its teeth into Carlin's hand, knocking him down and dragging him overboard, the fisherman told Associated Press news agency.

Carlin was dragged 20 feet below the surface, he said, leaving him fearing the worst.

"After 15 seconds, I thought I was going to die," Carlin said. "I continued to struggle, but thought this is the way I was going to die. It was unbelievable to me."

Finally, the sea lion released him and he swam to the surface.

However, the animal had not finished and bit his foot as he made his escape.

There was a gash on his hand that required 20 stitches and he spent two days in hospital.

"So many times, you see videos of cute seals, sea lions, but I'm sharing what happened to me because I want parents to realise these are wild aggressive animals that can take you down," he said.

The incident has not dampened Carlin's enthusiasm for fishing. Three weeks later he has almost completed his recovery and hopes he can go fishing as soon as next week.