Reach Casts are used on streams where current differences affect the standard overhead cast. Depending upon the direction of the current, the caster will "reach" either to the left or the right so that the line falls to the tip of the rod which is away from the caster. The reach is most often done after the stop of the overhead cast but before the line hits the water and is also known as an air mend. The maximum mend will occur when the the reach is done immediately during the shooting of the line after the stop. If you wait, the mend will be less as the line hits the water prior to the reach and the fly will tend to travel towards you rather than to the targeted location on the water. Laying the line at an upstream angle with a reach cast will allow the fly to travel a longer length of water drag-free without mending. Any mending done while the fly is in the water will create an unnatural movement, particularly on a dry fly.
Suppose you have a lie of fish and you want to put the fly 2-3 feet above the fish and get a drag-free drift. If upstream is to your right, you use a Right Reach cast. If the upstream is to your left, you use a Left Reach cast. Strip out about 6 feet of extra line to compensate for your reach. Make a false cast over your target and a normal backcast. Now on the next overhead cast complete the cast as normal with a stop to shoot the line. Upon making the stop, bring the rod to the right or left as the line is shooting. This is one fluid motion. Since the line is shooting as you make the reach, the fly will continue to it's intended target. The line, however, will be at an upstream angle. Follow the movement of the line and fly with the rod at the same speed as the current. This will give you a drag-free drift with no slack line in the water. Any strike will be immediately detected.
Reach Casts are also is usefull in presenting the flies from a different angle. For instance, an upstream boulder sheltering fish might entail laying the line over the rock in order to get the fly to position itself behind the boulder. This would immediately cause drag. A reach cast will position the fly in the same desired location but the line will fall to the side of the rock rather than over it.
Reach Up and Reach Down Mends
The Reach Down mend is generally used in up-current situations. It is similar to a puddle cast in that it results in extra line "s"-curved in the water. On the Reach Down mend, stop the rod about 60 degrees above the horizontal on the forward cast. Then reach down with the rod tip placing the midsection of the flyline into the water. The fly and remaining line will puddle into s-shaped curves between the point you dropped the line into the water and the intended target of the fly. These curves will allow a drag-free presentation among various currents as it is flowing downstream.
The Reach Up mend is generally used for down-current presentations. It will mend the line upstream by raising the rod tip up as in a roll cast.Then, by lowering the rod tip and feeding the line, you can present the fly to a lie of fish downstream with no drag and good accuracy. As in the the Reach Left and Reach Right Casts, the Reach Up mend is an air mend that brings the line back towards the caster before the fly line or fly reach the water.
The Reach Up and Reach Down mends can be combined with the Right Reach and Left Reach casts by various degrees to resolve many different current situations that you might encounter on the stream.