All fly fishers have their go-to spots. Spots they feel are productive; spots that give them confidence. Some people like to fish riffles. Some people like to fish up against the banks. Everyone likes to fish plunge pools.

And for good reason. Generally, these spots are the deepest, widest, and fishiest places in a river. But why?

Here are three facts about these spots, three reasons why fish love them, and three ways to effectively fish plunge pools:

1.1         A plunge pool is simply the bottom of a source of dropping water. In nature, waterfalls create plunge pools. Through man-made means, plunge pools exist under dam spillways. There are a number of factors that determine the nature of the pool. The height of the fall, the volume of water, and the composition of the streambed are most important.

1.2         While the rapidly moving water itself does encourage erosion, the sediment and debris that the falling water carries is much more abrasive to the riverbed below the source. The gravel or sand at the bottom is constantly shifting and scouring the bottom, while simultaneously being refreshed from upstream.

1.3         The flow of the falling water is not uni-directional. That is to say, it doesn’t just “go downstream.” The force kicks water and sediment back upstream, carving out a cave below/behind the falls. For this reason, even the smallest spillways and drops can be deadly to waders and boaters.

2.1         Fish are only looking for a few things in this world. Shelter is one of them. Sensibly, they want to hide from things that can eat them. Between the aforementioned caving and other, smaller crevices, plunge pools offer a bevy of cracks and crevices for fish to find solace.

2.2         If a waterfall can move and hold a lot of small rocks, it can move and hold a lot of small macroinvertebrates. It is also a spot that a larger, opportunistic fish might wait for a larger, incapacitated food source to come tumbling by.

2.3         Shelter and food are always necessary. For a brief time every year, spawning takes precedence. For most fish this means access to gravelly substrate – the kind that gets pushed out the back of plunge pools to form riffles and runs below. If a fish has these reproductive resources available, it can and will make a pool home.

3.1         The obvious spot to cast is right into the froth and fray of the waterfall. That makes sense, as that is the path any food from upstream would be traveling. However, the churning currents make keeping dries afloat and detecting strikes on nymphs difficult. A good play here is a weighted streamer. This might only be a size 10 on a small mountain stream, but something with weight is necessary to probe that undercut and resist the pounding flows.

3.2         The best places for a dry fly are right on the edge of the boil. Casting around the periphery of the angry water allows your fly to float a variety of trajectories that could entice a fish. By systematically working around the falls, you’re also improving your odds of fish from all over the pool noticing your presentation.

3.3         Although the tail out isn’t as glamorous as the plunge pool itself, there are often fish back there. These fish don’t have to fight as much current, and also don’t have to make snap decisions. A more subdued approach – such as a drifted nymph – is a great technique. Casting up into the deep, slower pool gives the nymph a chance to sink before it bounces through the riffles.

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This was a simple and cursory look at plunge pools, why fish like them, and how to approach them. At the same time, perhaps it gave you a little more insight or a different perspective regarding these angler- and fish-favorite spots.