Suppose you are standing at the edge of a deep stream with the current running from right to left. There are high trees close behind and on both sides, and grass and rocks along the shore line to the sides, so you can’t get any back cast in the air.
Standing by the bank as you are, a roll cast from the downstream side would catch on the grass and rocks along the shoreline. You are boxed in, but good, on every side except straight across-stream. Just then a big brook trout starts rising steadily against the far side of the river about fifty feet straight across. What do you do?
Well, there’s a very famous old English method made-to-order for this condition. It’s called the Spey cast technique —a variation of the roll cast. To make the Spey, after taking in any slack line, raise your rod tip in its down-stream plane to get the line well on top of the water.
After turning to the right, facing across-stream towards the rising trout, make a slight switch with your rod top that jumps your line up-stream and deposits it on the water just above you and far enough to your right to be clear of the plane in which your rod and line have to travel in making a fresh forward roll cast across-stream.
On this small switch up-stream stop your rod after it has passed the vertical and gone 22 1/2 degrees beyond that on the up-stream side. You now convert this up-stream switching action into a slow circling motion of the rod tip round to the left until it has reached a position behind you, tilted slightly to the right, and in a plane in which the forward cast across-stream has to be made. From this position you make an ordinary roll cast across stream to the rising trout.
This fly casting technique Spey cast sounds complicated on paper, but actually it isn’t hard to do—and when you need it, nothing else will do.
If you were in a similar position on the opposite bank of the river you can make a Spey cast equally well by bringing your up-stream switch of the rod to the left; and then making a roll cast straight across the river from a rod position tilted slightly to the left.