What are the disadvantages of building dams?

Answer 1

For the time it takes to fill the dam, there'd be no flow of water downstream. Might be awkward for someone in that direction who'd been relying on that water.

Depending on size, the area upstreams of the wall will be flooded. Kinda awkward for someone using that area of land.

A dam will prevent any fish from travelling up & down the river.

Answer 2

Buildind dams:

pros:

stops flooding, and its helpful towards big cities

cons:

people have to move like the one lake in china.

harmful to the world enviromental people.
Damming creates stagnant water, and can flood a decently-sized area due to the flow issues whch often result from damming. On the bright side, though, the biome which results from that same stagnation of the water tends to be teeming with life, and fish! Just wear plenty of bug repellent when it is warm out.

Answer 3

The main disadvantage of a levee is the possibility of failure. The failure of the levees around New Orleans in the aftermath of Hurricane Katrina were responsible for at least 1,000 deaths.