Why did Brazil destroy a natural wonder of the world waterfall for a dam ?

Answer 1

Brazil does have one of the seven natural wonders of the world, but it's not any waterfall, nor was it ever. It's the Harbor of Rio de Janeiro. Brazil's natural wonder would never be any waterfall because Victoria Falls between Zambia and Zimbabwe occupies the waterfall spot on the list.

Moreover, Brazil didn't destroy any waterfall with a dam. At best, it stopped it or lessened a waterfall. It's not destroyed because it's still there. If the dam comes down, that waterfall will be fully restored and back to being what it was. What Brazil did destroy is the ecosystem of the area that is now flooded because of the dam.

Why did it build the dam? I don't know. You didn't say what dam it was or what waterfall you're referring to. The most common reason is to generate hydroelectric power while also controlling flooding of areas prone to flooding or flash-flooding.