Lost is a Federal-owned dam located in Natrona, Wyoming, specifically in the city of SUSSEX. Built in 1966, Lost serves multiple purposes including fire protection, stock, small fish pond, and flood risk reduction along the Lost Creek. The earth dam stands at a height of 29 feet with a hydraulic height of 24 feet and a structural height of 29 feet, storing a maximum of 40 acre-feet with a normal storage capacity of 23 acre-feet.

With a low hazard potential and fair condition assessment, Lost has a spillway width of 100 feet and a maximum discharge of 372 cubic feet per second. The dam, primarily made of earth and stone core, covers a surface area of 3 acres with a drainage area of 0.7 square miles. Despite its moderate risk assessment rating, Lost remains a vital structure for water resource management and climate adaptation efforts in the region, requiring regular inspections every five years to ensure its continued safety and reliability.