Ask the River Oracle: If fishing is slow, how often should I change flies on the water?

Coast to coast, year in and year out, this is probably the question we receive the most from fly fishers. When our go-to fly patterns don't produce fish, and the hot patterns sold by the local fly shop don't get the fish to rise, when do you know it is time to change out flies? In a demonstration of Albert Einstein's definition of insanity, we often grit our teeth and continue to cast the same stale fly patterns with the vain hope of better results. This question isn't one that can be answered with a stopwatch, routinely cutting off and retying when the alarm chimes every 15 minutes, but is one that we will need to be determined based on the cues and guidance from mother nature when we are on the water. 

Don't Fish Blind - Sample the Water
No one would say that the most successful fly fishers get to the water, open their fly box, close their eyes tightly, and completely at random select one or two flies to tie on. When you read this, the notion is ridiculous, but this is essentially how many fly fishermen select the flies they fish. We have all been guilty of just tying on a trusted fly pattern or taking the word of a local shop without ever taking a minute to observe the bugs in and on the water. If you do not sample the bugs on the water when you are fishing, you will always be fishing blind!

Equal in importance to your fly rod and reel, and a necessity for every fly fisher, is an invertebrate seine. Simple to use, and less than the cost of a couple flies in the local shop, an invertebrate seine allows you to quickly and easily see which bugs are under the water, hatching, or flying around the river. If you take a moment to sample the water when you first get to the water, or as fish shift their attention to a new food source, you will be much more likely to choose a good match the first go round and it will be less likely you will need to change flies frequently. Without sampling, you might as well switch out your flies every 5 minutes, and each consecutive guess will continue to have an equally low probability of success. The answer to which bugs are in the water and therefore which flies have a greater probability of success is right beneath the surface of the water, and the seine is the fly fisher's key to matching the hatch!

Learn to Speak Trout

The fish always follow the food. As the bugs leave the bottom of the river and swim towards the surface to hatch, the trout will ascend from the riverbed in pursuit. As the emerging mayfly struggles from its nymphal skin and reaches its wings into the air for the first time, the trout will roll on the emerging duns at the surface of the water. When the mayfly spinners return to the river to lay their eggs and then expire on the surface of the water, the trout will greet them with open mouths. Therefore, as anglers, we need to learn to observe the feeding behavior of trout, and take their lead as to when it is time to change up our flies and match the next stage of the hatch.

So How Long Do I Wait?
Assuming that you have done your due diligence (sampling the water, observing the feeding behavior of trout, paying attention to your fly placement, drift, and depth) and your flies still aren't producing strikes or fish, we would recommend changing up your flies after 20-30 minutes of little to no action.