Water Quality Effects

1. Impoundments created by barriers cause stratification of temperature through the water column, making surface water warmer. This can lead to the warming of the river downstream
of the impoundment.
2. Dams and weirs act as pollution traps. As pollutants move downstream, they become trapped with fine sediment in the impoundments.
3. Impoundments trap nutrient movement and induce over-enrichment (eutrophication).
4. Algae blooms are common in impoundments and indicate too many nutrients in the water.
5. Organic materials trapped in the pond behind a dam use up more oxygen during decomposition than an equivalent area within the river. This results in a reduction of oxygen to downstream reaches.
6. Nitrogen gas super saturation can occur as water spills over a barrier into turbulent water.
7. Warming of water behind dams leads to increased bacterial concentrations, such as fecal coliforms.