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How can dams and diversions change a lake’s water budget?

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lake Lake Ann in North Cascades National Park, Washington, U.S., viewed from the park's Maple Loop Trail. The North Cascades National Park is a large wilderness area that preserves majestic mountain scenery, snowfields, glaciers, and other unique natural features.

Dams and water diversions significantly alter a lake’s water budget by modifying the natural inflow and outflow of water within a watershed. These engineering interventions are primarily used to manage water resources for power production, flood control, and water supply, but they often trigger complex environmental consequences.1

Impacts on the Water Budget

Storage and Outflow: Damming a river or a lake outlet increases local water storage. However, this larger surface area can lead to increased evaporation losses.1
Diversions: Diverting water into or out of a basin directly changes the volume of water available. For example, water may be diverted out of a system for human use or into a system from another watershed to supplement supply, both of which affect lake levels.12
Downstream Effects: Altering flow regimes can cause unintended consequences, such as the lowering of water levels in other lakes within the same system.1

Environmental Consequences

Beyond the water budget, these changes can disrupt ecology and physical features, including:
* Erosion and Sedimentation: Changes in flow can increase shore erosion or cause sediment to block harbours.13
* Biological and Thermal Impacts: Dams may restrict fish movement, flood bird breeding areas, and alter the thermal climate of downstream waters.1