A gut is a slough, or a narrow little canal that worms it's way to the larger body of water, be that a river, lake, bay, etc. Guts are sometimes dry, sometimes filled with water, according to the level of the larger body of water.
To be clear, I never shot a duck out of a motorboat while under power. My son and I have one that will seriously run them down, but you would need to be on a large body of water. It's a 21' Allison with a custom built 2.5 Merc and a 14 x 23 x 28 prop. Couldn't no duck outrun that.
My duck killing boat is for jump shooting them, and I just drift with the current.

SRH