South Boulder Creek – 04/01/2020

Time: 11:00AM – 3:30PM

Location: Below Gross Reservoir

South Boulder Creek 04/01/2020 Photo Album

After a productive day on Tuesday on the Arkansas River, I noted that the weather forecast for Denver for Wednesday projected highs in the upper 60’s. Could my body and arm endure back to back days of fishing early in the 2020 season? There was only one way to find out. I made a trip to the South Boulder Creek for a day of fly fishing below Gross Reservoir.

The DWR graph indicated that flows were around 16 CFS, and I knew from experience that 16 CFS is low but amenable to decent fishing. When I arrived at the kayak parking lot, six vehicles preceded me, and I concluded that other Colorado fishermen were taking advantage of a nice day while social distancing. The dashboard temperature was 51 degrees, as I assembled my Orvis Access four weight and wrapped my light down North Face coat around my waste under my waders. I was hopeful that the sun would dominate and warm the air temperature in the canyon, but my down coat was a safety net in case that scenario did not unfold.

I hiked a good distance from the trailhead and passed four anglers along the way. Assuming each car contained one angler, I accounted for four of six, but when I reached one of my favorite pools, I jumped in knowing that a huge amount of open water was above me. As expected, the flows were on the low side, but the large pool in front of me was very attractive (check the photo album link for a video of the pool). I assessed the situation and decided to begin with a single dry fly. Splashing a large foam attractor and beadhead nymph was probably not an effective strategy in the low clear flows on April 1.

Looking Ahead

Surprisingly as I scanned the surface of the pool from left to right, I spotted a pair of subtle rises along the center current line. In response to this observation I gazed at the surface of the creek and the air space above, but I was unable to determine an obvious food source. A periodic breeze rustled the trees, so I opted to tie a size 18 parachute black ant to my line. The choice was not totally off base, as two separate trout rose to inspect the terrestrial, but each turned away at the last instant. Clearly the fish were tuned into surface food, but my ant was not on their menu.

I pondered the situation and considered my next move, and concurrently the number of feeding fish increased. I was standing below the tail of the pool near the left bank, and I could observe several quite nice trout eagerly looking toward the surface for a morning snack. I suspected that the object of their desire was midges, but I was unable to spot any to evaluate the size or color, so I gambled on my tried and true size 24 CDC BWO. In similar situations in the past the minuscule dry fly served me well in a variety of tiny insect hatch scenarios.

CDC Olive in Lip

I searched in my box for the smallest version and quickly knotted it to my 5X tippet. I began tossing casts directly upstream and angled to the right and drifted the small morsel through the pool with quite a few actively feeding trout. Between 11AM and noon I managed to land four trout on the CDC olive, so my choice was somewhat verified. I say somewhat, because I probably made twenty casts for each landed fish, and the one hour period included several temporary connections and a significant quantity of refusals. I never determined what caused the random takes in the face of so many rejections.

At noon I paused once again to assess my path forward. I was pleased with four trout in one hour of fishing, but I sensed that I could be doing better. The frequency of rises escalated even more, yet my fly was being ignored by some very aggressive feeders along the center current seam. The visible trout, that were hunkered down at the tail, were totally ignoring the drifts. I decided to experiment with some alternative offerings. Before doing so, however, I stretched my mesh over the mouth of the net and seined the water for a minute. The only thing that appeared was an empty midge larva that was a bit over 1/4 inch long. I also noticed a solitary spent wing black adult midge in the surface film, so I began cycling through my supply of tiny midge adults. My first alternative fly was a size 24 griffith’s gnat, and it generated three close looks, but the fish did not close their mouths. Next I experimented with a trico spinner with poly wings and a trico with CDC wings. These flies never even attracted inspections from the greedily feeding pool residents. I found one of my FP emergers, a gray bodied midge emerger that I tied for the Frying Pan river, and it was likewise ignored. In my small fly canister I spotted a tiny parachute adams and knotted that to my line. It produced a pair of last minute refusals, but again no success was forthcoming.

Again I considered the situation. The CDC BWO, while not a sure thing, was clearly my most successful pattern in the current circumstance. I returned to the blue winged olive theme, but tried a Klinkhammer BWO. One small brown near the tail of the pool recklessly charged to the surface and inhaled the Klinkhammer, and my optimism surged. Alas my elation was short lived, as the emerger blue winged olive floated unmolested through the upper sections of the pool for the next ten minutes.

Bringing It Closer

The pool was now alive with aggressively feeding trout, and I could see many in the upper section moving several feet to grab unidentifiable morsels from the surface. If a blue winged olive hatch were in progress, I surely would have noticed adults gliding into the atmosphere above the creek or floating among the currents. Despite this lack of evidence I returned to the fly that delivered some level of success, and I knotted another CDC olive to my tippet.

Although I was building quite an appetite, the active feeding in front of me precluded a lunch break. I began sending casts of the CDC olive to the various sections of the pool, and surprisingly I enjoyed sporadic favorable results. The fish count climbed from five to thirteen, and enough trout showed interest to vindicate the CDC olive as the fly to utilize. I estimate that 60% of the landed fish were rainbows and 40% were brown trout. The size of the fish was generally in the nine to twelve inch range. The rainbows were colored in spectacular fashion with brilliant crimson stripes and vivid spots and speckles throughout the length of their bodies.

Another Perfect Rainbow

By 1PM the pace of feeding slowed, and I decided to rest on the bank, warm my feet and eat my lunch. The shrinking number of rises directed my thoughts to the rest of the creek, and after lunch and an additional fifteen minutes in the pool, I decided to alter my approach. I removed the olive and replaced it with a size 14 Jake’s gulp beetle and then extended a section of 5X tippet from the bend and attached a soft hackle emerger with no bead. The beetle with an orange indicator would be my lead fly, and a pause or dip would indicate that the soft hackle had been intercepted.

Looking Down on You

I ran the beetle dry/dropper through the mid-section and upper portion of the pool, and two fish streaked toward the small wet fly but turned away at the last instant. I suspect the ploy might have worked with a smaller emerger, but I only had size 20’s in my possession. I finally decided to abandon the gorgeous pool to sample other South Boulder Creek areas. A nice small triangular riffle area existed just above the top of the pool, and the right border of the triangle reflected off a large exposed rock. I flicked the beetle to the top right area of the triangle, and as it slowly drifted toward the V next to the rock, a large mouth appeared and engulfed the foam terrestrial. Imagine my joy, when I netted a wild thirteen inch rainbow after a spirited battle.

Speckles Right Into Tail

Perhaps prospecting with the dry/dropper would extend my streak of outstanding fly fishing on April 1, but that scenario never materialized. I began to migrate upstream, but I vowed to be very selective about my target casting areas. It was readily apparent that the trout were concentrated in the deep pools perhaps as a result of the low flows. Only recently had the flows been raised to 16 CFS after a long span of trickles in the 7 – 10 CFS range. The beetle prompted two refusals in relatively marginal runs, and then I encountered another very attractive long smooth pool, and once again evidence of surface feeding appeared in the form of several rises near the center current seams. I lobbed the dry/dropper throughout the pool, but these trout were not interested. I stripped the flies in and quickly converted to the CDC olive once again, but my earlier magic could not be resurrected. In a desperation move I replaced the CDC tuft with a parachute black ant with a pink wing post, and a cast to the shelf to the right of the center current yielded an eleven inch brown trout that confidently moved six inches and sipped.

My watch told me that it was now approaching 3PM, so I skipped a long swath of unattractive water and approached an area that provided favorable results in previous visits to South Boulder Creek. I was along the left bank, when I encountered a small but deep pocket beneath an overhanging branch. This was not the type of water that produced earlier on April Fools’ Day, but I gazed into the deepest point, and spotted a fish. Would this trout respond to my ant in this overlooked and out of the way location? It was worth a try, so I flicked the ant slightly under the overhanging branch, and after a six inch drift, the shadow darted to the surface and consumed the black ant. I raised the rod and connected, and before I could feel smug about outwitting this hidden gem, it streaked toward the bank and under the branch and managed to free itself. I was sorely disappointed over my inability to conclude the highlight presentation, but I celebrated my effort nonetheless.


I continued upstream to some attractive deep pockets without success, and then I encountered a pair of young men with small buckets and a shovel. Were they panning for gold in South Boulder Creek? If so, this was a first. I took this as a sign that my day of fishing was complete, and I made the hike back to the parking lot and stowed my gear. When I began my return drive, I checked the temperature, and it was at a comfortable sixty degrees.

Wednesday April 1 evolved into my best day of 2020. I landed fifteen trout, and fourteen came from the pool that I began in. Anyone who follows this blog will recognize what a deviation this is for this avid angler. My fly fishing mantra is move, and I generally allocate three to five casts to likely places and then move on. To remain in one pool for 2.5 hours is a testament to the length of the hatch and the number of pool residents. I estimate that at least fifty trout were present in what may be the best pool on the stream. I never found the perfect fly, but the CDC BWO was close enough to produce thirteen trout, albeit with an enormous number of casts. Another anomaly for April 1 was the fact that all fifteen trout resulted from a dry fly; a rarity for this early in the season. Hopefully when the weather improves I will have an opportunity to return.

Fish Landed: 15

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