>>8491713You are correct that It was probably stolen and that the frame had serial number.
It's a Honda motorcycle from 1976.
>honda motorcycle 1976 cb750-2567080What I came up with is that someone stole the motorcycle. Removed and probably sold the parts and got rid of the frame.
But here is there problem. The river was not salty.
Observe it better. You'll see what he did to it.
And what makes you think it was a teen? Teenagers are usually clumsy.