Mysis

The Mysis Shrimp (Mysis diluviana) is not a true insect or even a true shrimp (it's an opossum shrimp), but it is the secret ingredient behind some of the most famous trophy trout fisheries in the West (e.g., the Frying Pan, the Blue, the Taylor). Introduced into reservoirs like Dillon and Ruedi to feed Kokanee salmon, these high-protein crustaceans get flushed through the bottom-release dams into the rivers below. The result? Trout that gorge on "steaks" year-round and grow to football shapes.

Mysis are deep-water dwelling crustaceans found in cold, deep lakes and reservoirs. They avoid light. In the reservoirs, they migrate to the surface at night and go deep during the day.

• The Tailwater Connection: They enter the river only when flushed through the dam. Because they prefer deep, cold water, bottom-release dams discharge them constantly.

Mysis abundance in the river is often consistent but can spike during high flows or specific dam operations. Trout in Mysis tailwaters essentially behave like livestock at a trough. They sit in the heavy current right below the spillway and open their mouths. Because Mysis are high in fat and protein, the trout grow incredibly fast and thick.

Seasonality Year-Round. The "Mysis Hatch" is a flow-dependent event, not seasonal.

Tactics

• Sight Fishing: The trout are usually visible. The fly—being transparent—is not. You must watch the fish strictly.
• Depth: You must be on the bottom. Heavy split shot or tungsten beads are required.
• Transparency: The best patterns use clear materials (epoxy, dental floss, saran wrap) to mimic the glassy body.
• The "White" Fly: When Mysis die, they turn white. A simple white thread body or dubbing can work wonders.
• Trailing: Often fished as the lead fly in a two-nymph rig, trailing a tiny midge.

Recommended Patterns

• Realistic: Epoxy Mysis, Tim's Mysis, Will's Epoxy Mysis.
• Simple: WD-40 (White/Clear), Candy Cane Mysis.
• Attractor: Joe's Mysis (often has a flash back).

Mysis are an introduced species in many Western reservoirs. While they created world-class tailwater fisheries, they have arguably disrupted the food webs in the lakes themselves (competing with Kokanee for zooplankton). In the river below, however, they are a critical food subsidy for trout.