RIVER REPORT
Big Thompson | at RMNP
The Big Thompson River in Rocky Mountain National Park (RMNP) is a renowned trout stream originating high in the park’s alpine lakes and flowing through dramatic mountain landscapes. This freestone river offers a diverse range of fishing experiences, from small stream angling in its upper stretches near Moraine Park to larger pools downstream. The river supports healthy populations of brown, brook, and rainbow trout, with excellent insect hatches including mayflies, caddisflies, and stoneflies during the summer months. Its clear waters and accessibility make it a favorite destination for both novice and experienced fly anglers.
CONDITIONS
Weather & Flow Data Reported From OpenWeather and USGS
Recent Reports
Big Thompson River in Rocky Mountain National Park – April Fly Fishing Report: As of early April, the Big Thompson River within Rocky Mountain National Park (RMNP) is beginning to thaw at lower elevations, particularly in areas like Moraine Park and Horseshoe Park, which are now largely ice-free. However, water levels remain low, necessitating a stealthy approach to avoid spooking fish. Anglers can expect hatches of midges and Blue-Winged Olives (BWOs) during warmer midday periods. Effective nymph patterns include Soft Hackle Sow Bugs, Perdigons, and CDC Pheasant Tails in sizes 16–20. For dry fly enthusiasts, Mole Flies and small Parachute Adams in sizes 18–22 can be productive during active hatches. Given the clear and shallow water conditions, employing light tippets (5x to 6x) and a cautious approach is advisable. Focusing efforts during the warmest parts of the day, typically late morning to early afternoon, can enhance success rates. Overall, the Big Thompson River in RMNP offers promising opportunities for anglers this April, especially in the lower elevation areas as they continue to thaw.
Water Flow Data
5 Day Outlook
BUGS
The Big Thompson’s insect life provides a smorgasbord for hungry trout. AvidMax recommends these key fly patterns:
THE FISHERY
The Big Thompson River in Rocky Mountain National Park offers anglers a pristine, high-altitude fishing experience, with wild trout and breathtaking scenery in one of Colorado’s most iconic landscapes.
Fish Species
The Big Thompson River in RMNP is home to native greenback cutthroat trout, as well as wild brown and brook trout. The greenbacks, a threatened species, are a unique highlight of this section and are often smaller, averaging 8-12 inches. These fish are a prized catch for fly anglers due to their rarity and beauty.
Unique Fishing Conditions
The river in RMNP flows through pristine alpine environments, offering small stream fishing with clear water, pocket water, and undercut banks. Fishing conditions vary with the seasons, with summer and early fall being the best times to fish due to lower flows and active insect hatches. Small dry flies, such as caddis, blue-winged olives, and attractor patterns like hoppers and ants, are very effective, especially during the warmer months.
Access and Regulations
The Big Thompson in RMNP is easily accessible through various park trails, particularly around Moraine Park and upstream toward the headwaters. RMNP requires a valid park entry pass and all fishing is regulated by catch-and-release for greenback cutthroat trout to protect this native species. Anglers should also use barbless hooks and be aware of the park’s special regulations to preserve the fishery for future generations.
TACTICS
AvidMax encourages anglers to explore their full repertoire on the Big Thompson:
Nymphing
Nymphing allows anglers to target trout feeding below the surface, with or without an indicator, making it an effective technique for covering deep runs and slow pools where fish are actively feeding on subsurface insects.
Dry Fly Fishing
Fishing with dry flies provides the ultimate surface experience, imitating adult insects and offering exciting visual strikes, particularly during hatches when trout are feeding on the water’s surface.
Streamer Fishing
Using streamers mimics baitfish and other larger prey, offering an aggressive approach that can entice bigger, predatory trout, especially when fishing deeper water or fast-moving currents.
SEASONS
Each season on the Big Thompson brings unique joys and challenges for AvidMax anglers:
Spring
Spring runoff can cause higher flows, but fishing near the banks and slower pools with stonefly and baetis nymphs is effective. Look for calmer pockets of water where trout take refuge from the fast current.
Summer
Summer offers fantastic dry fly fishing with hatches of caddis, PMDs, and terrestrials like ants and beetles. Early mornings and late evenings provide the best surface action in riffles and pocket water.
Fall
Fall is prime for targeting brown trout as they prepare to spawn, making streamers and small nymphs like baetis patterns highly effective. Focus on deeper pools and undercut banks where trout are more likely to hold.
Winter
Winter fishing is slower, but small midge and baetis nymphs can still produce fish in slower, deeper water. Target the warmest part of the day for the best chance of finding active trout.
REMEMBER
The Big Thompson River in Rocky Mountain National Park (RMNP) offers anglers a pristine, high-elevation fishing experience, with wild trout and stunning scenery. However, its delicate alpine ecosystem requires anglers to practice responsible fishing to help preserve its natural beauty and health.
Water Conditions
The river’s flows can vary with snowmelt, especially in the spring and early summer, making for higher water levels. Late summer and fall often provide the most consistent and manageable conditions for fishing.
Regulations
RMNP has strict fishing regulations, including catch-and-release areas and limits on tackle types, such as artificial flies and lures only. Be sure to review and follow all park regulations to protect the fishery.
Safety
The high-altitude environment means weather can change quickly, with storms or cold conditions moving in fast. Bring proper gear for changing weather and stay hydrated, as altitude can affect your energy and stamina.
COMMENTS
We want to hear from you! Have you fished this River or have any advice for fellow anglers?
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