RIO Mainstream Saltwater Line Targeted to the overall needs of the average fly fisher. RIO’s Mainstream saltwater fly lines have been developed to meet the overall needs of the average and novice fly fisher, and are designed to optimize rod performance with slightly heavier and shorter head lengths. Every Mainstream line undergoes the same rigorous production processes and quality control standards as all RIO fly lines, and is made in RIO’s Idaho manufacturing facility. Each saltwater line is built with a hard, saltwater coating for the best in performance. Slightly heavier than standard lines for easy loading Supple core with a warm water coating that stays slick in the heat