South Lake Tahoe, California - A swimming trip ended painfully for a man who was suddenly attacked by a group of otters while swimming in a small lake near Lake Tahoe in California.

Matt Leffers was swimming in the Serene Lakes when something grabbed his leg.

"I felt something bite my calf," he told KCRA 3.

He was bitten over and over and tried to swim faster and escape, "but there was the otter, popped up right in front of me, and then I was bit again," Leffers explained.

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His wife finally rushed to his aid on a paddle board, fished him out of the water, and took him to hospital. The results of the swim were sobering, as Leffers emerged with around 40 bloody bite wounds.

"These things were so aggressive that, literally, I felt like they wanted to kill me," Leffers said, adding that it was the "most terrifying experience" he had ever had.

The Californian Department of Fish and Wildlife would now investigate the case, as Leffers is the second victim of an otter attack at that lake this year.

It is suspected that the animals' aggressive behavior is due to the abundance of fish in the local lakes.