Smalma's nailed it...again. It's almost like he's been doing this for a long, long time
The freshwater is like a lid on top of the clear saltwater below it. Used to catch a few in the San Juans in the dirty water when the Nooksack would blow chunks. One year it was brown all the way out past Point Lawrence, but the fish were still biting just fine at the point. I wouldn't say it works all the time, but often enough to where you might want to at least make a tow to give a favorite spot a check before moving on.