When I guide with guests who wish to learn more about fly fishing or to sharpen their skills, I teach them two mantras: fish the edges & the foam is home. Finding fish is the most important part in fishing. However, you would be amazed at how many times I show up to a crowded beat on a river and see people ignoring the prime water, and instead, fishing water because they are observing an occasional fish feeding here and there. They are fishing with their eyes and not their river reading skills. Knowing how to find hidden fish in heavy water can yield big results.
Recently, I was on a popular beat of the Yampa River in downtown Steamboat Springs. I have a favorite spot that conceals a lot of very nice fish. My river log will tell you my success on the Yampa and much of it can be correlated to this particular spot among just a handful. The froggy pool above me had two anglers swinging patterns to no avail and the pool below me was occupied, as it usually is on a daily basis. Yet, right smack in the middle of the river lays my favorite spot hidden in plain sight. I wade across to begin my approach while thinking to myself that surely, someone had to have pounded this spot and my efforts might be to no avail. I made my second cast and hooked and landed a nice 18" brown. I hooked and landed a few more fish and broke off a large gator rolling rainbow. I know that this spot does get fished as I have removed many flies that have broken off in the snouts of fish here. Perhaps these fish had been hooked elsewhere and sought refuge in this rarely fished spot?
What makes that particular spot on the Yampa and other similar spots unique is that it contains well defined edges and foam lines. An edge is where differing current speeds slip past each other and are often bordered on one or both sides by heavy water. Steelheading anglers know this as a current seam and that is where steelhead like to hold or travel along. Edges can also be defined by channel morphology such as gravel bars and drop offs or converging currents. In short, it gives fish structure both above and below the water surface.
Fish need three conditions for basic survival. Cover from above, a steady predictable food source drifting within close proximity and respite from the current. Edges usually provide all three of these conditions. If you find edges that contain a bubble line or a foam line you have found an ideal location to probe with a tactical nymph. Bubble lines are a clear indication of a current feature that funnels everything drifting downstream into a reliable path and if one is located near an edge you have eliminated a lot of guesswork. You can read about foam lines here.
The image below is perhaps one of the best examples of what a very "edgy & foamy" section of river can look like. On the left is a gravel bar forming an edge with a heavy section of current forming the other edge. A foam raft near the top provides cover for fish and the bubble lines gives us a clue that there is a food path for the fish. This pool also provides cover from above and bowling ball sized boulders on the bottom providing a buffer from the current. You can see the size of the boulders middle upper right. I watched two anglers fish this pool before I reached it and I managed to catch a few more fish out of it before calling it a day.
Green areas are the prime spots within the confines of this edges to pay special attention to. Don't forget to fish both sides of a heavy current edge and any pockets whereabouts additional fish might be found.
This pool is another example of an edge. Here, converging currents create a hydraulic edge thus defining a feeding lane and cover from above. Fish will hold very near the fast water slipping away to intercept anything edible that might be coming down the pipeline. There is a special spot near the top center of this riffle where the fish are protected on both sides from current cover allowing them to move either left or right in search of food. Can you find the sweet spot?
It's worth attempting to fish the near side of this current edge however, heavy angling pressure will likely cause the fish to concentrate in the water seeing less pressure. I landed a 21" rainbow and 18" brown rainbow out of the green section of this beat.
Have fun out there looking for those edges both obvious and more subtle.