There are countless fly fishing techniques out there, and they all work well for the particular situation they are designed for. One technique called the tight line swing is especially effective for covering large areas of water efficiently.
Most common as a steelhead presentation, “swinging” flies can be applied to other fish as well if the scenario allows. Ideal swing water is a section of flowing river or stream called a “run”. A run is typically water flowing with enough current to keep a fly from sinking as it swings along a tight line arch from down & across casts. Runs that are about walking speed and relatively shallow are best for swinging.
An angler can start at the top of a run, and begin to extend casts toward the opposite bank at apx 45 degree angle downstream. As the fly swings across the current, it completes it’s swing and stops below the angler. This process can be repeated over and over once the maximum casting distance is reached, and with a few steps down between casts the angler can work down a section of river with fly probing every few yards of the run. The speed and depth of the fly can be controlled by mending line up or down as needed, depending on currents and speed of the water.
This presentation works well with “swimming” patterns such as leeches, buggers, streamers, etc. But it can also be effective for dry flies like caddis, crane flies, and really fun for mouse patterns as well. It’s a low maintenance/high efficiency way to fish for any species of fish where the water allows. Just remember that with a take on a tight line like this, not to set the hook on a grab. Allow the fish to take the fly, then gradually lift the rod. A big set or lift will often rip a fly out of a fishes mouth.