Lost Valley is a privately owned dam located in Fruitvale, Idaho, along Lost Creek and the Weiser River. Built in 1910, this Earth-type dam stands at 31.3 feet high and has a storage capacity of 9,583 acre-feet, serving various purposes beyond flood control and water supply. Despite its age, the dam has faced concerns over its high hazard potential and poor condition assessment, prompting regular inspections and enforcement measures by the Idaho Department of Water Resources.

The dam's hydraulic height of 23.1 feet and controlled spillway with a width of 21 feet indicate its capacity to manage maximum discharges of up to 505 cubic feet per second. However, its poor condition assessment and high hazard potential suggest a need for improved risk management measures to ensure the safety of surrounding communities. The dam's location within the Walla Walla District and its association with the Weiser River make it a critical water resource and climate focal point for enthusiasts and stakeholders in the region.

Lost Valley's historical significance, coupled with its current risk assessment as very high, highlights the importance of ongoing monitoring and maintenance efforts to prevent potential disasters. As climate change continues to affect water resources and infrastructure resilience, this dam serves as a reminder of the critical role that proactive management plays in safeguarding communities and ecosystems against the impacts of extreme weather events and changing hydrological conditions.