[https://youtu.be/zcUrUE6-ZCw](https://youtu.be/zcUrUE6-ZCw)
I just watched The B1M’s video on removing four dams in the northwest, and they said that the sediment buildup behind a dam is bad for the environment but didn’t say why. What’s wrong with it?
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Sediment is the material that rivers carry and deposit along their course.
However, when a dam is built, it blocks the natural flow of sediment downstream.
This causes several problems for the environment, such as:
* **Loss of reservoir storage**. The sediment accumulates behind the dam and reduces the water storage capacity and the life span of the reservoir.
* **Deprivation of downstream sediments**. The sediment that is trapped behind the dam is no longer available for the downstream river channel and floodplain. This affects the shape and stability of the riverbed, and the diversity and productivity of the aquatic habitats.
* **Increased erosion**. The water that is released from the dam is clear and sediment-free. This means that it has more power to erode the riverbed and banks downstream, causing erosion and degradation of the channel.
* **Changes in water quality**. The sediment behind the dam can affect the water quality in the reservoir and downstream. For example, it can release nutrients that cause algal blooms, or pollutants that contaminate the water.
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