Colorado Fly Fishing 4 min read

DIY Guide to Fly Fishing the Big Thompson River in Colorado

Ken Sperry

Posted by Ken Sperry

May 23, 2024

Big Thompson River Colorado

Known locally as “The Big T”, Big Thompson River makes it headwaters among the heights of the Rocky Mountain National Park in Forrest Canyon before making its way down the mountainside through Estes Park, then feeding into Lake Estes before winding along highway 34 all the way to Loveland, CO. If you are keen to fish the headwaters, it is best to only make the journey in good weather midsummer, and then if and only if you are an experienced backpacker or hiker.

The trails near Forrest Canyon are treacherous even under the best of conditions, and they can be downright lethal in bad weather. Downstream of Forrest canyon though, there is some truly excellent fishing to be had, especially for those in search of rainbows, cutthroats, and browns.

About Big Thompson River

Fly Fishing Big Thompson River in Rocky Mountain National Park

Big Thompson River below Forrest Canyon is best known for its free stone stream fishing, so pocket water and riffles abound up and down the length of the river along Highway 34. Keep an eye out for the private property markers along the river banks though, as there are sections of the Big T that are strictly off limits to pedestrians and anglers alike. The trout in Big Thompson River are largely born in the wild and range in size from 10-12 inches. The river has not been stocked since the mid 1990’s.

If you aren’t intimidated by steeper, faster water and love to fish pocket water and riffles, the Big Thompson River is definitely a fly fishing destination for you.

Big Thompson River Map and Fishing Access Sites

map of fishing access spots on the Big Thompson River in Rocky Mountain National Park

Get Directions to the Fishing Access Points shown above with the DIY Fly Fishing Map

Best Places to Fish the Big Thompson River

The safest access point to the Upper Big T is definitely Moraine Park, and fishing is best upstream along the trails and streams that feed into the Big Thompson River throughout the park. It can get a little marshy during runoff and after heavy rains, so plan accordingly if you are looking to hike in search of your ideal fishing spot. If you do decide to fish among the meadow lands in Moraine Park, keep in mind that you need to approach quietly so as not to spook the fish, as there is little cover and brush nearby. The best fishing on the river is below Lake Estes is along Highway 34, as there is more public access and the river is consistently free stone stream fishing for the majority of its run all the through Idlewild Dam to Viestenz-Smith Park.

The river does tend to take a steeper grade the further downstream you go, but overall the pockets and riffles here yield some very large trout for those willing to brave the more difficult terrain.

Be mindful of the private property that dots the length of the Big T along the tailwater section, and a good rule to follow is that the riverbank on the highway side is usually public, but the banks opposite Highway 34 are not.

Big Thompson River Flow and Current Conditions


  • Temperature: 51.8 ° F
  • Streamflow: 72.1 ft³/s
  • Gage height: 4.75 ft
Temperature GraphStreamflow GraphGage height Graph

Best Time to Fish the Big Thompson River

Provided you steer clear of Forrest Canyon in the winter, fishing is solid all year round along the length of the Big T. Time of day doesn’t seem to affect the fishing all that much either, especially in the summer and fall when they are feeding to store up for the long winter. The October caddis hatch is the best of the year, so a fall visit to the Big T. is recommended for best results. Bear in mind that crowds will be at their peak in the summer and fall, but you can find isolated pockets with fast fishing if you are willing to hike a bit further off the beaten path.

Best Flies for Big Thompson River

The major hatches on the Big Thompson River are midges, BWOs, caddis, stoneflies, and even some tricos here and there. Be sure to match the hatch as best you can, and check with a local shop before setting out to ensure you’ve got what you need.

Here are the recommended flies listed by order of importance.

  • Hopper (tan #8-10)
  • Elk Wing Caddis (dark #14,#16,#18)
  • CDC Loopwing Quill Emerger (baetis #16-22)
  • Rosenbauer Parachute Beetle (peacock #10 – 18)
  • Smith’s Crippled Emerger (salt and pepper #20-24)
  • CDC Emerging Caddis (dark brown#16)
  • Pheasant Tail Nymph (dark #18)
  • Caddis pupas (dark #14-18)
  • Prince Nymph (peacock #12- 20)
  • Midge pupa (black #18 – 26)

Gear Recommendations

Experts recommend a 8-1/2 foot 4-weight fly rod for the Big T.  Definitely pack your chest high waders. The water is cold year round thanks to its mountainous headwaters, so be prepared to layer up, too.

Big Thompson River Fishing Reports

There are a number of area fly shops and on-line retailers that publish Big Thompson River fly fishing reports. A few to check out are listed below.

Fishing Regulations

Standard Colorado Division of Wildlife regulations apply to the majority of the river, but there is a Catch-and-Release only stretch for 9 miles below Lake Estes all the way to the Waltonia Bridge, and only artificial flies and lures are permitted on this section of the river. 

Trip Planning Tips

Access to the Big Thompson River is only a 2 hour drive northwest of Denver, and you can fine ample accommodations of every variety in Boulder, Estes Park, Loveland, and Grand Lake. You can even camp right in Moraine Park if you don’t mind roughing it for a few days.

There are also numerous hunting and fishing cabin rentals available in the surrounding area. Don’t forget to check out vacation rentals if you visit during the off-season for skiing either, as you can sometimes snag an unexpected bargain on a place to stay by renting a ski chalet or lodge when bookings are less frequent.

Looking for more places to fish? Visit our DIY Guide to the Best Fly Fishing in Colorado.

Feature image by Wusel007