If the salinity goes below about 5 ppm the trout start to leave. The river channel is about 30+ feet deep and the trout will stay in the area because the deeper water is saltier. If we ever get a big rain [~6"+] up north of Lake Charles, it could "flush out" the trout out of the Prien Lake area for a while.
http://waterdata.usgs.gov/la/nwis/uv...te_no=08017044