Time: 10:30AM – 4:00PM
Location: Below Gross Reservoir
A slow day on Wednesday on the Big Thompson River concerned me, so I resolved to target high elevation headwater streams and tailwaters until the weather cooled off a bit. As I perused stream flows prior to the Big Thompson trip, I noticed that South Boulder Creek below Gross Reservoir was reduced to 41 cfs. During a trip in early spring with flows at 30 cfs, I enjoyed a wonderful day, so I decided to make the short trip. South Boulder Creek is a tailwater, so it suited my recent resolution.
I left the house by 8:15 and after over an hour drive, I climbed into my waders and assembled my Sage four weight and departed down the steep trail to the creek. Unlike Wednesday the temperature was in the upper fifties as I began my hike, and high clouds blocked the sun and created a cool summer day in the mountains. The cloudy sky and intermittent breeze caused me to wear my raincoat for added warmth for nearly my entire day on the water.
Five other vehicles populated the upper parking lot, so I hiked for nearly an hour to position myself away from other fishermen. I was on the water and casting by 10:30, and I began with a yellow stimulator. The fish were either too cold to eat, or my fly was not recognized as food, so I exchanged the stimulator for a size 14 gray deer hair caddis. This fly was also ignored by the South Boulder Creek trout, so I once again opted for the dry/dropper technique. I knotted a tan pool toy to my line as the top fly, and below it I added a salvation nymph. As is normally the case, the nymph attracted attention and by the time I paused to eat my lunch along the side of the stream, I built the fish tally to six. Most of the morning landed fish were brown trout in the nine to ten inch range, and all except one impetuous pool toy eater snatched the salvation from the drift.
I finished my lunch at noon and resumed fishing, but I was curious if a second nymph might attract more interest. I inserted a beadhead hares ear above the salvation, and it did seem to boost the catch rate. As I paused to photograph one of the fish landed after lunch, the salvation somehow broke off, and since three successive trout grabbed the hares ear, I decided to preserve my salvation stock. I copied the Wednesday legacy ploy, and inserted the size 12 gray wet fly with a copper wire rib. This fly delivered two decent fish, but then its effectiveness seemed to wane, so I revisited the archives and tied a dark cahill wet fly to my line.
Again the antique wet fly revival paid off, as the dark cahill yielded four nice brown trout, and the fish counter climbed to the mid-teens. I began to skip the marginal pockets, and focused all my attention on deep runs and slots as well as pools. The most effective approach seemed to be casting across and allowing the flies to drift along deep current seams with a lift at the end. Of course the beadhead hares ear was also connecting with fish during the wet fly renaissance.
By 2PM I decided to return to the trusted combination of the beadhead hares ear and salvation nymph. I sensed that perhaps a pale morning dun hatch might be approaching, and I hoped that the salvation would imitate the active PMD nymphs. The move paid off, and I built the fish count to twenty-three by 3PM with many fish grabbing the salvation, as it plunked into the water at the top of deep pockets and runs. Twenty-three fish was a fine day, and I was feeling quite weary and faced a long hike back out of the canyon. so I contemplated quitting early.
As this thought passed through my head, however, I approached a gorgeous deep and wide pool. The main current divided the pool nearly in half with shelf pools on both sides. I was moving upstream along the right bank, and the top of my side was a bit wider and contained some swirling currents. Before I could cast my dry/dropper to the inviting area above me, I observed three or four rises. I scanned the air in case some obvious insect was spurring the sudden surface activity, but nothing was evident. I waited a bit longer, and a small fish slashed at something five feet above me and to the right. It appeared that the fish rejected the natural insect, because I could see a natural riding low in the film. I took a couple steps to look at the live insect more closely, and as it got trapped in a slow spot in front of a log, I scooped it with my hand.
Upon close examination I discovered that the mayfly was a size twenty blue winged olive. This caused me to take the plunge. I clipped off the three fly dry/dropper arrangement and switched to a single CDC blue winged olive size 22. I was sure I matched the hatch, but the fish destroyed my confidence. As four or five fish continued to rise in front of me, they totally ignored my imitation. I stopped casting and watched more intently, and I realized that the rises were actually the dorsal fins of the trout breaking the surface, as it seemed the trout were snatching emergers subsurface.
Could there be a concurrent pale morning dun hatch, and I happened to spot the less prolific blue winged olive? I tested this theory and tied a size 18 cinnamon comparadun to my line, but this was not the solution to the riddle. I debated trying an RS2 or soft hackle emerger, but before I could make this change, I observed two green drakes, as they floated up from the surface of the stream. Would the trout respond to a huge green drake, even though they appeared to be tuned into tiny emergers? I did not have anything to lose, so I tied a size 14 green drake comparadun with no rib to my line and began to cast it to the area of visible rises above me.
Initially it was refused, but then as it danced in some swirly deeper water behind an exposed rock and next to the main current, a fish slashed at it and sucked it in! I landed a spunky rainbow trout and my first South Boulder Creek green drake victim of the year. The next half hour was amazing. As I focused on the area above me on the right side of the center current, I spotted occasional rises near the tail on the other side of the main seam. I pivoted and delivered downstream casts to this area. The change in tactics proved to be a stroke of genius, and I landed seven more trout on the green drake comparadun. I was dumbfounded by the number of fish in the left shelf pool, and nearly all were rainbow trout in the 9 – 12 inch range. The other fascinating facet to this phase of my day was how aggressively the fish attacked the comparadun. Several fish darted from the depths and lunged at the fly with their momentum taking them above the water. In one case I began to lift to cast, and a fish apparently feared its meal was about to flee, so it launched and grabbed the fly.
Finally after landing seven fish from the productive pool, I went five minutes without a take, so I moved to the next area which featured a nice riffle over moderate depth. The green drake yielded its eighth hungry victim here, but then it ceased to produce. I was curious if green drakes hatched in other segments of the stream, so I moved greater distances in search of obvious juicy pools, where I could more easily spot rises and follow my fly. Alas, the strategy was sound, but I was unable to net additional fish, so I called it quits by 4 o’clock and made the forty-five minute hike back to the car.
What a great day Thursday proved to be! Cool overcast weather allowed fairly consistent action through the day punctuated by the green drake frenzy over the last hour. When I returned home and checked the flows, I discovered that the water managers doubled the flows from 41 cfs to 85 cfs during the morning. I was skeptical that the velocity was 41 cfs when I tried to cross, and my skepticism was vindicated. Nevertheless I enjoyed a fantastic day on South Boulder Creek, and as the dog days of August continue, I plan to return.
Fish Landed: 31