Actually, Banks of the Ohio kills its victim by stabbing rather than drowning too - at least in the versions I'm familiar with.

Here's the key verse from Olivia Newton John's recording:

"I held a knife against his breast
As into my arms he pressed
He cried "my love, don't you murder me
I'm not prepared for eternity"

And here's Johnny Cash's account of the same moment:

"I plunged a knife into her breast
And told her she was going to rest
She cried "Oh Willy, don't murder me
I'm not prepared for eternity."

That final line about being "not prepared for eternity" occurs in Knoxville Girl and its predecessors too, of course, which is one of the reasons I say Banks may be part of the same song family.