Why Trout Move | Understanding Freshwater Migrations

They don't run to the ocean, but they still move.

Face to face with a brook trout in August – likely on its way to spawn. | Photo by Mark Pickrel

When we talk about migratory trout, we’re usually talking about steelhead or sea-run browns – the anadromous ones. Their migrations are wildly impressive – traveling several hundred miles to reach the ocean from their freshwater spawning grounds. But freshwater trout migrate too, and we should talk about it more often! 

Short-Distance Runners

Freshwater trout migrations typically span just a few hundred yards and tens of miles. They’re not covering the distance that their anadromous relatives do, but they, too, will seek out new water for a number of reasons. 

Spawning

The primary driver of freshwater trout migrations is spawning. Trout eggs require specific conditions to survive: gravel beds with consistent flows of cold, clean, highly oxygenated water, which are most often found in small tributaries or headwater streams. 

Many trout live in stretches of river that don’t have ideal spawning conditions, so they’ll run up to a better spot when it comes time to spawn. A good spot may be just around a bend, or it might be several miles upstream. 

Feeding

Unlike Pacific salmon – many of which die after spawning – freshwater trout can spawn multiple times over the course of a lifetime. It begs the question: Why wouldn’t they just stay in their spawning grounds year-round? The answer has to do with food. 

The small streams where trout tend to spawn often have a limited food supply, and post-spawn trout need to feed to replenish their spent energy stores – the lack of food is a strong incentive to migrate back down to their home ranges. 

Water Temps & Flows

Trout are sensitive fish – most prefer water temps between 45° and 60°, and they want to stay in that range year-round. When water heats up in the summer, trout will move upstream to find cooler, shaded water. When it gets frigid in the winter, they’ll typically move downstream to find slower-moving water with deep holes – where temperatures are more consistent. 

Trout are sensitive to flows. When water gets high during runoff, fish move to areas with more stable holding spots. When flows get low during the summer heat, they move upstream to find water with the oxygen levels they need to thrive. 

What It Means for Trout Fishing

Get a handle on trout migration patterns, and you’ll have a much better shot at finding them year-round. The stretch of river overflowing with fish in June might be pretty quiet come November – freshwater trout move, and there will be times when you might have to move with them.