Andy Hill of Missoula and his wife were floating under a bridge on the Clark Fork River near East Missoula Sunday when the man landed on him, KECI-TV reported.
"Suddenly I had intense pain and was under water," Hill said.
"There was a guy on my lap and he rolled off my lap and he just kept apologizing saying 'I'm sorry, I'm sorry, I'm sorry,'" Hill said.
The man swam Hill to shore, still on the inner tube, and the man's friend helped Hill as well.
Hill suffered broken bones in both lower legs and a cracked femur in his left leg and will likely spend the rest of the summer in a wheelchair or on crutches.
But he's been able to keep his sense of humor.
"Who does this happen to?" asked Hill, laughing. "I don't know of anybody this has ever happened to."
Missoula County authorities say the man who jumped could be charged.