I'd be careful about generalizing too much about never fishing turbid water. You can catch cutthroat and salmon in muddy or seaweed filled water under some circumstances. The #1 reason to fish turbid water is if there are baitfish in close to the beach using the low visibility water for cover. A few stories:
Once at a beach in the Nisqually Reach area I was staring out at the water while relaxing, and was disappointed to see the incoming tide was kicking up silt. I had my rod in my truck but I wasn't going to waste my time fishing that muddy flat with low visibility water. I quickly changed my mind about 20 minutes later when a small group of Bonaparte's gulls started taking baitfish out of the muddy shallow waters about 10 feet out from the beach. I grabbed my gear and waded out into the silty water and started blind casting a baitfish pattern. As I retrieved my first cast I saw a large pair of terrorized eyes swimming directly at me, just a few feet from my stripping basket. It was a herring with its swim bladder apparently damaged. A couple of seconds later a large cutthroat savagely struck it from below, missed, then hit it again. With my hands trembling I backed up toward shore and started fanning out casts into the murk. Within an hour I managed to land 2 very well fed cutthroat and missed some others.
That same year I visited a north sound beach that fished well on an outgoing tide. I arrived at the peak of the high tide and made some phone calls, waiting for the tide to ebb and take away the copious amounts of floating seaweed and eelgrass. While talking on the phone my jaw dropped as the large area of floating debris started to erupt in violent slashes and jumps of feeding cutthroat and salmon. Apparently a large group of juvenile sandlance had started to shelter amongst the seaweed and the predators were starting to gorge themselves. I hung up the phone and started tossing out a baitfish pattern and managed to land one nice cutthroat and a lot of salad. The outgoing tide rapidly took away the seaweed, baitfish, and all those feeding cutthroat and salmon. It was one of the most amazing feeding frenzies I've ever seen, but it wouldn't have happened without the seaweed.
Last story. I was fishing a Case Inlet beach in March '07 looking for cutthroat feeding on chum fry. I found the chum fry in very close to shore sheltering in shallow water. They were still tiny and weak swimmers, but there were large schools of them. The tide was going out fast and the wind started to blow into shore, kicking up silt from the muddy bottom. The visibility of the water 6 feet out from the beach was poor at best and the chum fry were hanging out in the turbid water. A few cutthroat and small resident silvers were in the area, but the fishing was sporadic and I had to cover a lot of beach. The most effective approach was to walk the beach and start casting parallel to the shore and strip my fly slowly. Over the course of the day I landed about 10 cutthroat and silvers, the majority of them in close to shore in the silty water using a variety of small baitfish patterns. The cutthroat were using the muddy water and wind blown waves to cover their shallow water feeding attacks, and the chum fry were just trying not to be seen. One of these muddy water cutties was very large:
