By understanding trout metabolism and feeding behavior in winter, anglers like you can adjust your tactics, choose the right gear, and enjoy productive cold-season fishing with confidence.
What happens at 35°F (near-freezing water)
Trout are cold-blooded, ectothermic, so their metabolism slows way down.
- They can survive on very little food
- Digestion is slow
- Activity is minimal
- Some trout can go weeks to months with little or no feeding if they have enough stored energy
Estimated caloric intake for survival at 35°F:
- Small trout (.25lb.): 2–5 calories per day
- Medium trout (1 lb): 8–15 calories per day
- Large trout (2.2 lb): 15–30 calories per day
These are survival calorie level estimates, assuming the fish is mostly resting and not stressed. With this information you can extrapolate the caloric needs for the size trout available in your streams. The fish can consume enough calories on a warm afternoon to last all week. For reference, one #20 midge larva equals roughly 0.06 calories and a #16 Mayfly Nymph equals 0.3 calories. At 35°F, one scud or a few midges can meet a trout’s daily needs. At 55°F, that same trout must eat several dozen insects per day
For more in-depth information on the calories available in Aquatic Insects, Check out our article “The Aquatic Insects: How many calories are they worth?”.
(Caloric estimates taken from “Trout” by C.Fox 1967 which were based on studies conducted by Penn State University.)
How Cold Water Changes Insect Availability
Cold water doesn’t eliminate aquatic insect life—it changes where and how that food becomes available to trout. During winter, surface activity is limited and noticeable hatch events are rare. Most aquatic insects remain close to the streambed, sheltering beneath rocks, within cobble, or slightly buried in the substrate. Because of this, trout feed primarily on benthic drift—aquatic organisms that are dislodged from the bottom and carried by the current.
Cold-adapted insects, particularly chironomid (midge) larvae, remain active along the bottom even in frigid water. When slightly warmer conditions or natural disturbances occur, some pupae enter the drift, creating brief but reliable feeding opportunities for trout.
What This Means for You on the Water
In winter, trout are operating with a greatly reduced metabolic demand. Being ectothermic, they lack both the energy and the caloric need to chase food. While you may occasionally see midges—or even a sparse caddis or Little Dark Stonefly emergence—fish rarely respond to surface activity when water temperatures are below 40°F. Consistent surface feeding typically doesn’t begin until water temperatures climb above 45°F.
When I arrive at the stream, the first thing I do is use my thermometer to check the water temperature and record it. If the temperature is below 40°F, I focus on slow-moving water with at least two to three feet of depth and a cobblestone bottom. These areas provide both cover and energy-efficient feeding lanes. Nymph selection is determined by current speed and depth, and while experience helps narrow the choices, achieving the right drift often requires constant attention and adjustment.
Your goal is to present nymphs that drift naturally along the bottom. They should neither drag across the substrate nor ride above the bottom more than a few inches. Using light tippet (5x-6x fluorocarbon) allows the fly to move more naturally in the subtle currents near the bottom, where trout hold in winter. It’s common to adjust weight several times in a single pool to achieve the correct drift.
Positioning matters as much as presentation. Cold trout are still wary, so careful wading and thoughtful positioning are essential. Remember, the first fish you spook is usually the one you could have caught.
Winter nymph strikes are subtle. The most successful anglers set the hook often—if it looks like a take, treat it as one. Euro-nymphing and swing-nymph techniques, both taught in our On the Stream Schools, are especially effective for maintaining contact and detecting light strikes. I prefer Sighter Wax or Murray’s Strike Indicators because they don’t float, allowing the fly to drift naturally in the slower currents near the streambed—exactly where winter trout are holding and feeding.
What equipment do I need to have with me?
- Stream Thermometer
- Assortment of nymphs
- Fluorocarbon Tippet Material in 5x and 6x
- Trout Nymphing or Euronymphing leaders
- Murray’s Indicators or Sighter Wax
- Split Shot Assortment
- 2, 3 or 4 weight fly rod with a delicate tip
How Trout Feed During Winter: Biology, Metabolism, and What It Means for Anglers – Part One of Two