Dams offer other advantages. They are most commonly used to generate electricity through water power, to charge water-supply systems, and to create artificial lakes for recreation.
However, dams can harm the environment. They interfere with fish migration and habitat for other wildlife by reducing water flow.
Downstream human communities also may suffer from diminished water resources. Worldwide, more than 200 rivers flow through two or more countries. Friction over water resources constantly threatens conflict in the Middle East. No country is so dependent on a single lifeline as Egypt is on the Nilewhose source is in Ethiopia. Eighty percent of Iraqs water originates outside its borders. Headwaters of the Tigris and Euphrates, which flow through Syria and Iraq, are largely controlled by Turkey. The two downstream countries have complained about massive Turkish dam-building programs.
In seeking to control flooding by manipulating water flow, people create new sets of problems.