Turbidity and photosynthesis

Here's the mv. Leonard L. Whittington about to go under the Robert C. Byrd Bridge, a.k.a. the 6th Street bridge, over the Ohio River at Huntington, W.Va., this week.

I particularly like how the water changes color as the barges pass through. It's mostly brown because of the heavy rains we've had this past week. Somewhere a professor has a chart of the depth of the photosynthesis zone as it varies with increasing turbidity. But I'm not looking for it right now.