We have all been there, fishing a foam eddy on a river where a thick white cloud of foam is hiding a pile of trout. Sometimes the foam is broken up by a trout's nose poking through like someone is dropping in a marbles in the water. These are a great places for trout to live. They offer protection from above with the foam acting as a shield from predators above. The currents are generally slow and great place for trout to hang out with their friends and not have to work out. Food also gets caught in these eddies and goes around and around making it an endless buffet of insects for the trout.
Eddies can also be frustrating for the angler as dry flies are hard to see and keep floating in the foam. There is usually many different currents going in various directions making it hard to manage your line and keep your fly floating properly. Try these five tips to catch more fish in those eddies.
Understanding the currents that you are fishing is a major factor in fishing back eddies. Realize that trout are constantly looking into the current for their next meal. So you might need to face the opposite way and cast downstream and have your flies drift back to you to get the proper drift. Try to decipher which way the trout are facing and place your flies a few feet above them without throwing your fly line on top of them, just your leader.
Try and get as close as possible to the trout without spooking them. By doing this you will increase your chances of having to fight many of the other currents that are usually found in back eddies. The foam should help camouflage your approach and let you sneak closer than when fishing the regular currents.
Many times you may witness the foam bulging or a trout's nose poking through the foam as they pick off food trapped in the foam. I have spent countless hours over the years trying to fool these trout and I have had more success fishing a dry/dropper rig then trying to match the hatch. First of all smaller dries size 14 and above are invisible in thick foam. Many times they also float on top of the foam instead of on the water. When I can see trout feeding in thick foam I usually tie on a good size fly (something like a size 10 stimulator or such) and drop a small nymph off it relatively short (12-16"). The bigger dry will be more visible for the angler and easier to detect strikes.
With difficult currents pulling your flies in different directions you can buy yourself some additional "drift" or time by lengthening up your leader. By increasing your leader length it will take more time for your leader to straighten out and then start to "drag". I am not a huge fan of throwing really long leaders but there is always a time and a place to add additional tippet to a regular 9' leader. By adding an additional couple of feet in these slower currents you can buy yourself an another 3-5 seconds which is usually all that is needed to fish these back eddies efficiently.
Another effective technique for fishing back eddies is called "short leashing". This nymphing technique utilizes using two nymphs under an indicator at short distance. Generally most anglers using this technique fish their nymphs 2.5-3 ft below an indicator. Flies vary with the seasons and hatches but I generally have one heavier, larger fly on top and then something that matches what I see happening on the water. For instance, I really like nymphs with tungsten beads. I may fish a size 14 Czech nymph on top and drop off a olive micro mayfly in the spring time when the Blue winged olives are coming off. This technique really works well on the Missouri River for me and I usually already have an extra rod ready for when we hit the various eddies. The presentation doesn't have to perfect and the trout will chase the nymphs even when they swing in the current.
Give these techniques a try the next time you fish a back eddy and I believe that your success rate will increase.