A weir is a small dam built across a river or stream to control water flow. It helps manage water levels, allowing for irrigation, flood control, and maintaining aquatic habitats. Weirs can also create a calm area for fish to spawn and can be used to measure water flow. Weirs come in various designs, including broad-crested and sharp-crested types. They are often made from materials like concrete or stone. In addition to their practical uses, weirs can enhance the beauty of natural landscapes, making them popular in parks and recreational areas, as well as in hydropower generation.