Why do tailwaters below dams hold trout in places otherwise too warm?

Because a bottom-release dam is an artificial spring on an industrial scale. Water drawn from deep in the reservoir — the cold, stratified bottom layer — comes out at 8–14 °C (46–57 °F) all summer, creating kilometers of trout-grade temperature in regions where every natural river runs too warm. This is how world-class rainbow fisheries exist far south of natural trout latitude. The habitat has quirks: temperature is stable but flows swing with power generation (a safety issue — know the release schedule), the cold water can lag oxygen right at the dam, and the trout-viable zone fades downstream as the river warms back up, often within 15–30 km (10–20 mi) in hot climates.

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