Dewey is a private water resource located in Declo, Idaho, serving primarily for irrigation purposes. The dam, completed in 1913, spans 2300 feet in length and has a height of 30.1 feet, with a storage capacity of 225 acre-feet. It is situated on Marsh Creek, a tributary of the Snake River, in Cassia County, Idaho.

This significant structure is regulated by the Idaho Department of Water Resources and undergoes regular state inspections, with a satisfactory condition assessment as of July 2017. Despite its age, Dewey is classified with a moderate risk level, indicating the need for ongoing risk management measures. The dam is considered to have a significant hazard potential, prompting the importance of emergency preparedness and potential inundation maps.

Water resource and climate enthusiasts will find Dewey to be an intriguing site for its historical significance and role in supporting agricultural irrigation in the region. With its earth dam construction and stone core, Dewey stands as a testament to early 20th-century water management practices and continues to play a crucial role in water storage and distribution for the surrounding area.