Sorry, guess I have a bit of dry humor.
It is sort of a local thing. When the Arkansas river starts her runoff this time of year, even 6" of water can take you off your feet. In most places you can wade across as the fly fishermen do prior to runoff.
Once rafting kicks in, a "swimmer" is someone who gets thrown out of the raft and it can be very dangerous. Therefore, you would not want to swim in the river until say late August when it slows back down again.
I guess the humor is, it doesn't matter how deep it is, you don't want to go in at all.
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