The most popular line weight the world over, a 5 weight has the power to make learning to cast easy, and allows you to fish bigger rivers and lakes. If you're just starting out, this would be the minimum weight we'd suggest starting with. With a 5, you'll be able to get the fly where it needs to be to catch fish, sooner than if you start with something lighter. A 5 weight is ideal for casting a bit of weight or an air resistant indicator and it can cope well in wind. It's not the ideal choice, but it can be used for the majority of lake fishing as well. A true all-rounder.
