Sometimes human actions can have both positive and negative environmental impacts.

a negative impact of a large, hydroelectric dam is that it backs up water sometimes for miles behind it, destroying natural habitat that once was there.

but a positive environmental impact of a dam is that

Besides the negative environmental impact of dams there are also many positive environmental impact of dams. Dams help to prevent flooding and the water can be stored to provide energy like the hydro electric power

Explanation:

When a dam is constructed in a area whenever there is drought in the areas the stored water in the dam will be helpful for irrigation and drinking purpose. The water stored are made to fall on the turbines and produce hydro electric power

Dams even help to prevent floods excess of water will be stored in the dam and hence the effect of flooding will be reduced and the water stored can be used efficiently

These are some of the positive environmental impacts of the dam

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