Rio Technical Euro Nymph for the modern nymph angler. 

RIO’s Technical Euro Nymph line is designed for the modern nymph angler. It's built on a monofilament core that creates a stiff, slick line for quick feeding and less line sag between the rod guides, and an ultra-thin diameter to maximize sensitivity, and for lightning-fast hook sets. In addition, the core extends past the front end of the line to become a leader—resulting in no knots to get caught in the guides. The level line can be cut to length (from the back), allowing anglers to tune the line to the perfect length. The leader is .013" in diameter, pink to be easily seen, and is level, so can also be cut and tuned for varying situations.