A dam is a structure built across a stream or river to hold water back. Dams can be used to store water, control flooding, and generate electricity. According to studies and research, it has been found that dams were originated during the times of ancient Mesopotamians. Dams provided farmers with a steady source of water to irrigate crops. The biggest dam in India is called Bhakra Nangal Dam is located in the state of Himachal Pradesh and Punjab and the oldest dam is called Kallanai Dam which is built across the Kaveri river of Tamil Nadu.