Story highlights Eugene Finney says he was hit in the back by a large object underwater

The injury was treated at a hospital where doctors made an "incidental discovery" of a tumor

(CNN) It's not clear what caused a deep gash down Eugene Finney's back while swimming in the ocean with his daughter, but it's clear the brush with danger helped save his life.

Finney, from Fitchburg, Massachusetts, was visiting his parents in Huntington Beach, California, in July with his two kids and girlfriend, Emeline McKeown, who would be meeting his parents for the first time.

The Finney family shares a love of the ocean. Eugene grew up on the Jersey Shore. Finney's parents, now retired, fell in love with Huntington Beach and decided to make it their home after his father was stationed at the nearby Naval Weapons Station Seal Beach. They took McKeown and the kids for a day of sunbathing and swimming. Eugene's parents bought Temple, 10, and Turner, 6, boogie boards.

The family arrived at the beach midmorning and before Temple took the new boogie board for its maiden voyage, she asked her dad to go for a swim. They swam about 100 yards off shore amid 7- to 9-foot waves and found themselves in water about 10- to 15-feet deep. Finney turned and saw a large wave approaching and quickly grabbed Temple to dive under the breaking wave.

When he tried to surface, he was hit by a large object. "I was hit in the back hard. Really hard. I've never been hit that hard in my life," Finney said.

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