What is the main concern when constructing a dam? 

A dam is a barrier that is built across a river or waterway to hold back and control the flow of water. The stored water can be used for a variety of purposes such as irrigation, hydroelectric power generation, flood control, water storage, and recreation. 

Safety is the main concern when constructing a dam, as a failure of a dam can result in loss of life, property damage, and environmental consequences. To ensure safety, dams are designed and built to withstand natural disasters, such as earthquakes and floods, and are regularly monitored and maintained.