Fly Fishing The Big Thompson River in Rocky Mountain National Park, Colorado

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The Big "T" is one of the largest rivers on the Front Range, due in part to the enormous number of drainages that come together to form it. The other reason this is a big river is due to the 13-mile, 9-foot diameter Alva B. Adams Tunnel that brings water from Shadow Mountain Reservoir on the Western Slope, through the Continental Divide, and into the Big Thompson River.

The Upper Big Thompson River begins in the mountains of Rocky Mountain National Park and flows east through Estes Park before being stored in Lake Estes, along with the water diverted from the Western Slope.

This stretch of river is a typical mountain freestone stream that is only ice-free for 4-5 months of the year. Inside Rocky Mountain National Park, fishing typically begins at Moraine Park. The stream has cut through this wide open meadow that has a large resident herd of elk, and created some very deep cut banks. While most trout in the Park do not exceed 14 inches, this stretch of water can hold some very big trout. Letting the current take a olive bugger back under the bank may require more than the usual 5x tippets used here.

Hatches during the year are as follows:

• Midges: Year Round
• Baetis: April / May & September / October
• Green Drake: July / August
• Red Quill : July / August
• Caddis: June through September
• Terrestrials: July through September
• Stoneflies: June through August

Hanging a olive or black midge below a Parachute Adams is almost always a good choice. If nothing else, the Adams makes a great strike indicator! Throughout the Park, smaller is better. Yes, there are some #6 stoneflies in the Upper Big T, but you'll catch more fish with #14-18 Dries and #18-22 nymphs. You shouldn't need to go smaller than 5x tippet, but you may want to use fluorocarbon as these fish do get a lot of pressure.

The Lower Big Thompson, meaning below the dam on Estes Lake, plunges down a rocky canyon that has a plethora of public water. Most of the canyon is National Forest land with pockets of private property all along its length. Although it is a tailwater, it will dirty up quickly as it enters the canyon. With almost daily afternoon thunderstorms, the further you drive down the canyon, the dirtier and warmer the water will get. During peak runoff (late May through mid June) the water below the dam can be very dirty and the flows quite high (700+ CFS).

During the summer, if you find the water to be over 70 degrees, please don't fish it. The oxygen levels in the water are so low that even briefly playing a fish has a high likelihood of killing the fish you release.

The stream can easily be waded, and during the middle of summer, wet waded, averaging 100-200 CFS. The rocks can be slippery so felt or studs are recommended. The only people who float the Big Thompson are a fly fishers crazy friends, the kayakers, and only then during certain flows.

The hatches listed above apply to this stretch of water, too, but the bug size is typically at least 1 size larger. The evening caddis hatches and afternoon Green Drake & Red Quill hatches provide the dry fly enthusiast with plenty of opportunities.

This river has lots of large rocks, deep runs, and plenty of holding water. Coupled with food being more readily available, more months being icefree, this section of river is home to some truly large rainbow and brown trout.

Planning a trip to Rocky Mountain National Park? Visit our on-line fly store for a complete selection of flies before you head out.