Nielson, also known as Arapahoe, is a privately owned dam located in Fremont, Wyoming, specifically in the city of East Thermopolis. Completed in 1934, this earth dam serves multiple purposes including fire protection, stock watering, small fish pond, and irrigation. It stands at a height of 15 feet with a hydraulic height of 10 feet and a length of 1250 feet, creating a storage capacity of 385 acre-feet.

Despite its low hazard potential, Nielson is rated as having poor condition as of the last inspection in July 2019. The dam has a spillway width of 30 feet and an uncontrolled spillway type. It is regulated by the State Engineer's Office and is subject to regular inspections, enforcement, and permitting by the state regulatory agency. While the risk assessment for Nielson is moderate, with a rating of 3, there are currently no inundation maps prepared or emergency action plan in place.

Water resource and climate enthusiasts should keep an eye on Nielson for any updates regarding its condition and risk management measures. With its strategic location on the W Fork Sheep Creek, this dam plays a crucial role in the local water supply and ecosystem. Continued monitoring and maintenance will be essential to ensure the safety and functionality of Nielson for the surrounding community and environment.