Howard A. Hanson Dam, Embankment dam in King County, United States.

Howard A. Hanson Dam is an embankment dam crossing Eagle Gorge that rises above the Green River and uses a concrete spillway to manage water flow. The structure holds water across a drainage basin and helps regulate downstream conditions throughout the year.

Construction began in 1959 with an explosive blast and finished ahead of schedule in 1961. The project was designed to address recurring flood problems that threatened the valley.

The dam transformed the Green River Valley from flood-prone farmlands into a developed area with warehouses, industrial facilities, and residential communities.

The dam lies within the Tacoma watershed and public access is not allowed, so the structure and reservoir cannot be visited; recreation proponents have contested this restriction for years. Water released from the dam is diverted to a purification facility 3 miles (5 km) downstream for civil consumption. The reservoir is kept near empty in winter and drawn down in March to hold water.

The concrete spillway on the dam's left side, fitted with two 45 by 30 foot Tainter gates, has never been used to pass floodwater. The outlet tunnel at the base, controlled by two smaller Tainter gates, handles all routine releases.