Yeah I've fished it twice now in the past month, since they shut the flood gates and went to a power demand generation schedule (since it's been fishable). The water is basically chocolate milk at the moment, I'd say maybe 6 inches of visibility. The first time I fished it I caught about 15 trout. I fished again last weekend and only caught about 4. Both times most of the fish were caught within a half mile of the dam. I walked and fish all the way down to the south end of Watts on Saturday and even see a fish down there, so I'd doubt if Marval is very productive at all. Plus I know a little over a year ago the ODWC decided to stop stocking near the Marval area at the resort's request.
If you're gonna go, your time would probably be better spent up close to the dam. Just a fair warning though the water is pretty nasty. I almost feel like it was worse the second time around.