What the Big Thompson offers and when to fish it

The Big Thompson River runs east from the Continental Divide through Rocky Mountain National Park and into the foothills below Estes Park, making it one of the most accessible trout streams in the region. The stretch most anglers fish starts where the river exits the park near Moraine Park and continues downstream through the town of Estes Park and into the canyon below. You will find brown trout and rainbow trout throughout, with cutthroat in the higher sections inside the park.

The river fishes best from late May through September. Spring runoff from snowmelt keeps the water high and cold through mid-June, making the fish sluggish and the current dangerous. By late June, flows drop enough to read the water and present flies effectively. Summer brings consistent hatches—caddis in June and July, pale morning duns in July and August, and terrestrials in late summer. Fall can be excellent in September before water temperatures drop and fish become less active.

Water levels and clarity vary dramatically depending on recent rain and snowmelt. After heavy rain, the river turns brown and fishes poorly for two to three days. Check the USGS stream gauge for the Big Thompson near Drake before you drive up; flows above 500 cubic feet per second make wading difficult and nymphing the better choice over dry flies.

Key Takeaways

  • The Big Thompson holds brown and rainbow trout in town and cutthroat higher up, with the best fishing from late June through September when water levels drop below 500 cubic feet per second.
  • Access is easiest in Estes Park itself, where the river runs through town and alongside US Route 36, with several pullouts and a public park providing entry points.
  • Caddis and pale morning dun hatches dominate summer, but nymphing with small dark patterns works year-round when the water is clear.
  • The river canyon below Estes Park holds larger fish but requires scrambling down steep banks and careful wading in faster current.
  • A Colorado fishing license and a park pass (if entering Rocky Mountain National Park) are required; check current regulations for daily limits and fly-only sections.

Where to access the river in and around Estes Park

The town of Estes Park sits directly on the Big Thompson, and the easiest access is along US Route 36 as it runs through town. Pull off at Riverside Drive on the north side of town, where a paved path runs alongside the river for several blocks and connects to Riverside Park. This section is shallow and slower, good for beginners or when you want to avoid crowds. The water here is warmer and often cloudier than upstream sections, so fish tend to be less selective but also less abundant.

For more productive water, drive west on US 36 toward the park entrance and look for pullouts along the road where you can see the river. The stretch between Estes Park and the park boundary holds more fish and deeper pools. Parking is limited but available at several turnouts; arrive early on weekends. This section requires more wading skill because the current is faster and the bottom is rockier.

Inside Rocky Mountain National Park, the Big Thompson flows through Moraine Park and along the Bear Lake Road. You will need a park entrance pass, but the water here is colder, clearer, and holds cutthroat trout. The park restricts fishing to fly and lure only, and some sections are catch-and-release. The park website lists current regulations and any sections closed to fishing.

Below Estes Park, the river enters a steep canyon where the road pulls away from the water. Access here requires scrambling down banks or hiking in from trailheads. The fish are larger and more wary, but the effort keeps crowds light. The canyon is dangerous during high water and after rain; do not attempt it if the river is running high or if weather looks unstable.

Fly patterns and techniques that work year-round

Small nymphs work on the Big Thompson more days than anything else. Carry dark patterns in sizes 14 to 18—pheasant tail, hare's ear, and small stonefly nymphs in black or brown. Fish them on a dead drift near the bottom in deeper pools and runs. Add a small split shot or use a heavier nymph if the current is fast. A strike indicator helps you see takes when you cannot watch the fly directly.

When you see caddis in the air (usually in late afternoon in June and July), switch to a dry caddis pattern in tan or olive, size 14 to 16. Fish it in the current seams where the fast water meets slower water. Caddis do not sit still on the water, so a slight twitch or skate can trigger strikes. If nothing rises to a dry, drop a small nymph under the caddis as a dropper.

Pale morning duns hatch in mid-morning from July through August. Use a PMD dry in size 16 to 18 when you see duns on the water. If fish are rising but refusing your dry, try a smaller nymph or a parachute pattern that sits lower in the film. The hatch usually lasts one to two hours, so timing matters.

Terrestrials—ants, grasshoppers, and beetles—work well in August and September when the water is low and clear. Carry a few small ant patterns (size 16 to 18) and a hopper or two in size 10 to 12. Fish them along the banks where they might naturally fall into the water. Late summer is also a good time to fish small streamers if you want to cover more water and search for larger fish.

Regulations and what you need before you go

Colorado requires a fishing license for anyone 16 and older. You can purchase a one-day license, a five-day license, or an annual license through Colorado Parks and Wildlife. The license is valid statewide on all public water. You do not need a separate license for Rocky Mountain National Park, but you do need to pay the park entrance fee.

The Big Thompson has different regulations depending on where you fish. In Estes Park and the lower canyon, the river is open to all legal methods (fly, spin, bait) with a daily limit of four trout. Inside Rocky Mountain National Park, only fly and lure are allowed, and some sections are catch-and-release only. Check the park website or stop at the visitor center for current rules before you fish.

Wading boots with good grip are essential because the rocks are slippery and the current can be strong. Bring a net if you plan to keep fish; it makes handling and releasing easier. A small backpack with water, snacks, and a headlamp (if you fish late) keeps you comfortable during a long day. The sun reflects off the water and rocks, so sunscreen and polarized sunglasses reduce glare and help you spot fish.

When water levels make the Big Thompson unfishable

Spring runoff is the biggest obstacle. Snowmelt from the high country keeps the river high and cold through mid-June most years. The water turns milky from glacial silt, and the current is too fast to wade safely. Fish are also less active in cold water and do not feed aggressively. If you arrive in early June and the water looks brown and fast, plan to fish a smaller tributary or wait a few days for conditions to improve.

Heavy rain can turn the river unfishable overnight. A thunderstorm in the mountains can raise the level several feet in an hour. The water becomes opaque, and the current becomes dangerous. Wait at least two days after rain before returning; the river clears from the top down, so the upper sections near the park clear first. Check the USGS gauge before you drive up to confirm the water has dropped.

Late fall and winter bring low water and cold temperatures. By October, the water is often too cold for good fishing, and the air temperature makes a long day uncomfortable. Some anglers fish winter, but it requires patience and small flies. If you are new to the river, plan your trip for July or August when conditions are most forgiving.

Nearby alternatives if the Big Thompson is too high or crowded

The North Fork of the Big Thompson is smaller and often clears faster after rain. It joins the main river near Estes Park and holds smaller trout but fewer people. Access is from Forest Road 43 west of town; the road is rough but passable in a regular car.

Bear Lake inside Rocky Mountain National Park is a short walk from the parking area and holds cutthroat trout. It is not a river, but it fishes well when the Big Thompson is too high. The lake is also a good option if you want to avoid wading in current.

The South Fork of the Poudre River is about 30 minutes south and often fishes well when the Big Thompson is blown out. It is smaller and more technical, but it holds good numbers of brown trout. Access is from the Poudre Canyon Highway (Colorado 14) east of Fort Collins.

Frequently Asked Questions

Do I need a guide to fish the Big Thompson?

No. The river is accessible from the road, and the water is straightforward enough for self-guided fishing. A guide is helpful if you are new to the area or want to learn specific techniques, but many anglers fish it successfully on their own. Local fly shops in Estes Park can point you to good access points and current conditions.

What is the best time of day to fish?

Early morning and late afternoon are usually most productive because the light is lower and fish are more active. Midday can be slow, especially in summer when the sun is bright. If a hatch is happening, fish during the hatch regardless of time of day—usually mid-morning for pale morning duns and late afternoon for caddis.

Can I keep fish from the Big Thompson?

Yes, in the sections below the park. The daily limit is four trout. Inside Rocky Mountain National Park, some sections are catch-and-release only; check the park regulations before you fish. Many anglers practice catch-and-release on the Big Thompson to preserve the fishery, even where keeping is allowed.

Is the Big Thompson safe to wade?

The river is generally safe to wade when flows are below 500 cubic feet per second and the water is clear. Wear a wading belt and felt-soled boots for grip. Never wade alone, and do not attempt the canyon section during high water or after rain. The current can be deceptive, so test the bottom before committing your weight.

What should I do if I hook a large fish?

Keep your rod tip up and maintain steady pressure. Do not jerk or set the hook too hard on a 5-weight rod—the tippet will break. If the fish runs downstream, follow it if you can. Use your net to land it, and handle it gently if you plan to release it. Wet your hands before touching the fish to protect its protective coating.