Wyoming Drops Fall-Spawning Rainbows at Twin Buttes After Study
Wyoming Game and Fish stopped stocking fall-spawning rainbow trout at Twin Buttes Reservoir after Eagle Lake rainbows grew bigger and were caught more often.
The Wyoming Game and Fish Department has stopped stocking fall-spawning rainbow trout at Twin Buttes Reservoir near Laramie after a study found that Eagle Lake rainbows grew larger and ended up on anglers’ lines more often, according to a department report published by The Fishing Wire.
Twin Buttes will keep getting brown trout, Eagle Lake rainbows and cutthroat trout. The fall spawners, stocked as part of a test, are out of the rotation.
Why biologists tried a second rainbow strain
Twin Buttes is one of the Laramie Plains Lakes, a group of waters known for growing big fish quickly. Trout there cannot reproduce, and anglers keep many of the fish they catch, so the department restocks the lake from time to time. For years that meant Eagle Lake rainbows, browns and cutthroats.
Biologists noticed that fly and bait anglers did well catching Eagle Lake rainbows from shore in spring, when that strain spawns. They wanted to see whether a rainbow that spawns in fall could give shore anglers the same kind of fishing later in the year, so they added fall spawners to the stocking plan.
To tell the two strains apart, hatchery workers clipped the adipose fin on the fall-spawning fish while they were still juveniles. The adipose fin is a small fin on a trout’s back, and the clip let anglers and biologists tell the two strains apart at a glance.
What three years of netting and surveys showed
For more than three years, the department compared the strains using netting, creel surveys (in-person interviews with anglers at the lake) and an online survey. The results lined up:
- Eagle Lake rainbows averaged nearly 1.5 pounds heavier and more than 4.5 inches longer than the fall spawners.
- Anglers caught more Eagle Lake rainbows than fall spawners in both the interviews and the online surveys, which matched what biologists saw in their nets.
- The fall spawners never produced the hoped-for fall shore fishery. Biologists expected them to move toward the rocky area near the boat ramp in autumn, and they did not. The department says it is unclear why.
With Eagle Lake rainbows ahead on size, catch rates and angler success, managers dropped the fall-spawning strain from the Twin Buttes schedule.
How much anglers contributed
Hundreds of survey responses from local and visiting anglers went into the decision. A few people supplied a large share. One angler sent in nearly one-third of the spring 2025 responses and nearly one-fifth of the fall responses. Another reported a 6-hour outing in 2024 that produced 25 rainbows along with brown and cutthroat trout. Other anglers reported catching little.
Colter Brown, a Game and Fish fisheries biologist in the Laramie Region, said creel surveys show what anglers are “actually experiencing on the water,” something netting and measuring cannot capture.
What it means for Wyoming trout anglers
Anglers at Twin Buttes should see the same three species as before the experiment, with Eagle Lake rainbows as the stocked rainbow. A rainbow with a clipped adipose fin would be a fall spawner left over from the study.
The study is one small piece of a large program. In 2026 the department stocked more than 5 million fish in more than 350 waters across Wyoming, and biologists judge each stocking by fish numbers, average size, catch rates and how satisfied anglers are. At Twin Buttes, angler reports carried as much weight as the biological sampling, and the department says that data will keep shaping future decisions for the reservoir.
Source: The Fishing Wire
