tailwater

Tailwater is the body of water released from a dam's tailrace, the conduit that carries water away from the turbines and through the outlet works downstream of the dam. The tailwater downstream of a dam is affected by the reservoir level, turbine operations, and spillway releases, and its flow is typically regulated to meet flood control, power generation, and downstream water-supply objectives.

The released water often originates from the reservoir's depths and can be cooler and more oxygenated than river water downstream of the dam, producing a relatively stable thermal regime. Depending on stratification and intake depth, tailwaters can be cold and clear or more variable. Seasonal and daily operations can alter discharge volume.

Tailwaters can create productive fisheries by providing predictable flows and suitable temperatures, supporting species such as trout and smallmouth bass in some regions. However, dam operations can disrupt sediment transport, migration routes, and natural flood pulses, affecting downstream habitats. Some systems implement fish passages, selective withdrawal, and environmental flow releases to mitigate impacts. Tailwater areas are common for sport fishing, particularly fly fishing, due to steady flows and access.

Tailwaters pose hazards including strong currents, undercurrents, hydraulics near spillways, and floating debris. Operators balance multiple objectives: flood control, water supply, hydroelectric generation, and ecological considerations. Research and policy developments focus on maintaining ecological integrity while preserving dam benefits.