I don't think the water temperature our fish are caught from plays as much of a part as the preparation water temp (or brine). I've smoked summer walleyes with fantastic results, my neighbor's favorite smoked fish is a summer white bass (which is also my favorite fish for grilling), and dear ol' Dad used to smoke dogfish from the late summer into early fall... going back to the difference between flowing water or stagnant water, however, can be a MEGA-difference in flavor.