Not to be mistaken for the similarly named Reach mend cast, the Reach cast is another cast designed to eliminate drag from your fly to help it react more naturally during it's drift, only this time when casting across a current (often a uniformed current).
Most of these drag free drift casts can easily be performed on the end of a Spey cast, however, when explaining these casts I am going to approach them all from an Overhead cast perspective so as not to cause any confusion, but do bear in mind that combination casts can be of great benefit to the angler too.
To perform this cast, (when casting across a current) as you bring the rod tip to a positive stop in the forward delivery of your Overhead cast, reach your casting arm out and upstream to a position of up to 90 degrees from your target, the fly line should still land on the water in a relatively straight line between your rod tip and your fly. The only difference being, it will be in a straight line from a position upstream of you to your target and not in a straight line between you and your target as is usually the case.
This can be a great cast when fishing a dry fly downstream. "Why would I want to do that", I hear you say. Well, there are many areas on a river that you cannot access from a downstream position, to allow you to cast your dry fly upstream to a rising fish, for a drag free drift, small weirs for instance, which are often fantastic areas for good fish to sit and pick off the natural insect as it flows towards the lip of the weir (one of my favourite areas). This downstream method gives you the opportunity to follow your fly with your rod tip from an upstream position on it's voyage downstream (at the same pace as the current) and therefore not only eliminating any potential drag, but also allowing you to stay in contact with your fly line and fly throughout the drift in the event of a take.
When using this cast, shooting line into the cast is paramount (unless a very short cast is required) as this will assist with distance and prevent your fly from being pulled away (bouncing back) from it's intended target during the forward delivery as consideration must be given to the fact that you are also reaching upstream during the delivery which will in turn shorten the amount of line available to travel out in front of you, unless you shoot line into the cast during the upstream reach.
As with many of these casts I have focused mainly on one particular application for each, but in reality, many of these casts can be used in a variety of situations you will encounter whilst fishing.