No, that's probably not a flock of undersized American crows you see along the Arkansas River. They're probably appropriately named fish crows.
Slightly smaller than the common Kansas variety, fish crows generally have more sheen on their feathers. Their call is also different.
Common along coastal waters of the Gulf and Atlantic, they're increasing their numbers in Kansas. Fish crows often feed on dead fish or any hapless minnow, crayfish or other small animal in or near the water.
They can fly low to the water, dipping their bills below the surface as they glide to get a drink.