Neffs is a private irrigation structure located in Lyman, Utah, along the Cedar Creek river. Built in 1900, this earth dam stands at a hydraulic height of 9 feet and boasts a storage capacity of 80 acre-feet. The dam, with a length of 135 feet, serves the primary purpose of irrigation in the region, with a normal storage level of 50 acre-feet.

Owned privately and regulated by the Utah Division of Water Rights, Neffs is classified as having a low hazard potential and is not currently rated for its condition. The dam has undergone inspections every 5 years, with the last assessment conducted in February 2011. With its location in Wayne County, Utah, Neffs contributes to the water management infrastructure in the area and plays a crucial role in supporting agricultural activities in the region.