"...I take it this effect is achieved at a subtile boundary with different watersurface levels."
Nope. The water effect in MSTS is essentially useless for mountainous regions, or any area where there is significant fall in the terrain's valley floors. You're looking at modeled water.
"I've no experience of lumber mill logdams but would the water have been quite churned up and so more brown than blue?"
Quoting from my original post...
"Still some color tweaking to do."
I will be adjusting the water color some, but I'm not going to make it too sludgy. Scenically, I would prefer things to look a bit nicer than they did in real life.
This entire scene/effort is a "freebie" for you guys.
You see, after backing off and looking at Turners Bend, I felt it needed more "reason" for the attraction of the railroads into the region, so I am building a large sawmill at this location. This, in conjunction with two other large industries that will be on the connecting lines, justifies more "plausibility" within my modeling psyche.