Question

how construction of large dams becone a controversial issue

Answer 1

Construction of dams become controlversial issue becaue it needs more place, farms comes under it, aquatic animals has less place to travel, it is costly.
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Answer 2

Construction of large dams court controversy because it normally involves displacement of people, submerging pristine forested land, causing loss of habitat of fauna and loss of flora, among many other issues highlighted by environmentalists and activists.  

Mismanagement in controlling dam operations can also have far reaching negative consequences like flooding, loss to crop and other agriculture and loss of life and property.