Most Trout fishers know that water temperature affects a Trout but few know how temperature influences the Trout's behavior. This is a subject worthy of a lengthy article but for this blog let's focus on cold water.
As outside air temps drop, water temps follow. The first few weeks of fall weather can really be great fishing with temperatures on the drop, but not yet so cool that the water temperature slows down the Trout's activity level. Once cold weather has really set in, our waterways cool dramatically and the Trout's feeding and activity level slows with the cold water temps. On most rivers, water temperatures in the low forties or less bring sluggish fish found in slow, deep pools. Do not despair, they will take a fly but sometimes you have to hit them on the head (figuratively) since they won't move far to take a food item. Keep this in mind when prospecting for Trout. In the morning hours, when water temps are their coldest the fish will be lethargic so focus on slow deep water. As the day warms, expect the fish to become more active as the water temperature rises, even if the rise is only a couple of degrees. Once the rise has occurred riffles and runs that earlier in the morning were void of fish can come alive, especially if there is a hatch of insects to draw the attention of the Trout.
On a recent trip to North Carolina my friend and fishing partner George Daniel and I plied the waters of the Raven's Fork on the Cherokee Indian Reservation. The water was quite cold and very clear. This made it possible to sight fish a fair bit as well as cover likely holding lies while blind casting. In the morning hours the Trout were podded up in slow pools. By 2pm or so, some of the fish would migrate to riffle water to feed for a while and then return to the nearest slow pool when water temps drop in the evening. We targeted active fish by casting flies to fish that were either seen feeding or holding in riffles or pocket water.
Below is a picture of George fishing some of the shallow riffle water on the first fishing morning of the trip. As we "felt" our way through this piece of water, we quickly learned there were no feeding fish in the faster sections. If we were fishing this same stretch in May, things would be different. Trout often inhabit shallow riffles during prime water temperature ranges.
Once you find some fish, focus on getting flies down to their feeding depth and presenting the flies at the speed of the current in which the Trout are holding. Good searching patterns for most rivers in the fall include: Baetis nymphs, midge larva and pupa, scuds or sow bugs and attractor patterns like a Rainbow Warrior, Copper John or Lightning Bug. My favorite baetis is the Iron Lotus in olive (see earlier blog post), a great sow is the Tungsten Tailwater Sow Bug and good midges include zebra patterns or a Mercury Black Beauty.
Get out on the water, be "one with the rock" like George is in the picture below and take in some of the last days of trees with leaves...