Located in Niobrara, Wyoming, McMaster No. 4 is a privately owned irrigation dam on the Niobrara River. Built in 1966, this earth dam stands at a height of 14 feet and has a storage capacity of 248 acre-feet. With a surface area of 23 acres, it serves multiple purposes including fire protection, stock, and irrigation.

Managed by the State of Wyoming, McMaster No. 4 has a low hazard potential and is categorized as being in fair condition. It features an uncontrolled spillway with a width of 75 feet and an outlet gate equipped with a single valve. With a moderate risk assessment rating, this dam undergoes inspection every five years to ensure its structural integrity and safety.

Despite its remote location, McMaster No. 4 plays a crucial role in water resource management and agriculture in the region, highlighting the importance of maintaining and monitoring such infrastructure for the community and the environment.