Looks like a giant concrete pour. But seriously, how massive were those rocks pushed along like pebbles.Little too thick to drink, and a little to thin to plow, plus way too difficult to kayak. When kayaking, ya kinda prefer that the rocks hold still, otherwise it's a bit difficult to find the line, among other things.The rocks and mud make for a good illustration of why river beds, especially right at the bottom of a dam, fill up and need to be occasionally dredged.