Agate No 1, also known as Ball Reservoir, is a privately owned irrigation dam located in Elbert, Colorado. Built in 1890, this earth dam stands at a height of 18 feet and has a storage capacity of 3400 acre-feet. The dam, constructed with a stone core and resting on soil foundation, serves the primary purpose of irrigation along the East Bijou Creek-TR.

Despite its age, Agate No 1 has been well-maintained and is in satisfactory condition as of the last inspection in 2017. With a low hazard potential and a high risk assessment rating of 2, the dam presents a manageable level of risk. The absence of a spillway and presence of two slide gates for outlet control indicate the unique design features of this historic structure, which has seen modifications in 1925 to enhance its structural integrity.

The dam's location in Deer Trail, Colorado, highlights its importance in water resource management for the region. With a surface area of 286 acres and a drainage area of 25 square miles, Agate No 1 plays a crucial role in providing irrigation water to the surrounding agricultural lands. Enthusiasts of water resources and climate will find interest in the history and functionality of this key infrastructure within the Omaha District.