The Upper Delta Basin Enlargement, also known as No. 1 Tailings, is a privately owned earth dam located in Green River, Wyoming. Completed in 2013, this structure serves the primary purpose of storing tailings material, with a maximum storage capacity of 9992 acre-feet and a structural height of 40 feet. The dam has a fair condition assessment and a high hazard potential, requiring regular inspections to ensure safety.

Managed by the State of Wyoming and regulated by the SEO, the Upper Delta Basin Enlargement plays a crucial role in the management of water resources in the area. Situated along the Green River, it covers a surface area of 652 acres and has a drainage area of 0 acres. Despite its fair condition, the dam is equipped with outlet gates for controlled release of water and a spillway type that is not specified in the data.

Owned by a private entity and designed by Phillip Solseng, the Upper Delta Basin Enlargement is a significant infrastructure project in the region. With a history of inspections and maintenance, this dam continues to contribute to water management efforts in Sweetwater County, Wyoming. As climate change impacts water resources, structures like the Upper Delta Basin Enlargement become essential for ensuring water security and mitigating potential risks.