Fly Fishing the Big Thompson River in the Rocky Mountain National Park

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.

Where to Fish in the Upper Sections

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 an olive bugger back under the bank may require more than the usual 5x tippets used here.

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Flies for the Big Thompson

Hatches during the year are as follows:

Insects	Size	Best Seasons
Midges	18	Year Round
Baetis	18	April / May & September / October
Green Drake	16	July / August
Red Quill	16	July / August
Caddis	14-16	June – September
Terrestrials	10	July – September
Stoneflies	12	June – August

Hanging an 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.

Where to Fish in the Lower Section of the Big Thompson

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.

Best Streamflow and Temperatures

During peak runoff (late May through mid-June) the water below the dam can be very dirty and the flows quite high (700+ CFS). I would recommend flow rates less than 100 CFS using the streamflow gage at Loveland. Link to gage HERE

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.

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Wading the Big Thompson

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 ice-free, this section of river is home to some truly large rainbow and brown trout.

Flyshops and Guides

Estes Park offers some options for advise with some fly shops and guide services.

• Kirk’s Fly Shop is probably the best known in the area. Some “insider” intel along with flies and guides.
• Fly Fish Estes Park is a guide service that calls the Big Thompson home. Checkout what they have to offer HERE.
• If you’re looking for something a bit more family friendly, I’d checkout Trout Haven Fishing Pond. Lodging and some entertainment for the family. They’ve got all kinds of lodging available, as an added bonus this is a perfect spot for heading into the mountains.

One More Cast in the Big “T”

The Big Thompson offers a fly fishing paradise for anglers with its abundance of public water and National Forest land. The sections in Moraine Park offer small water solitude, while below Estes Lake Dam the river picks up speed and typifies a rocky mountain canyon river.