Rio Fly Fishing Fly Line Mainstream Bass/Pike/Pinfish Wf6F Fishing Line, Yellow RIOs Mainstream series of fly lines have been developed to meet the overall needs of the average and novice fly fisher Every Mainstream line undergoes the same rigorous production processes and quality control standards as all RIO fly lines, and is made in RIOs Idaho manufacturing facility. All fly lines are made with pride in our Idaho Fall facility Designed to optimize rod performance with slightly heavier and shorter head lengths. Each saltwater line is built with a hard, saltwater coating for the best in performance.