O'Brien North, also known as Reservoir 4, is a private-owned dam located in Itasca County, Minnesota. Completed in 1972, this earth dam stands at 49 feet high and serves primarily for tailings purposes related to mining activities in the area. With a storage capacity of 2550 acre-feet and a drainage area of 8 square miles, O'Brien North plays a crucial role in managing water resources in the region.

Managed by the Minnesota Department of Natural Resources, O'Brien North is regulated, inspected, and enforced by state agencies to ensure its safety and integrity. The dam has a significant hazard potential and has been assessed to be in fair condition as of August 2015. Its last inspection in June 2018 indicated that it meets regulatory guidelines, but further risk assessments and emergency preparedness measures may need to be undertaken to enhance its resilience to potential disasters.

Situated on O'Brien Creek, O'Brien North is a key component of the water infrastructure in the area, providing vital flood control and water storage capabilities. As climate change continues to impact the region, ensuring the safety and effectiveness of dams like O'Brien North becomes increasingly important for water resource and climate enthusiasts alike.