USS Nyanza was a large steamer purchased by the Union Navy during the American Civil War.

She was assigned by the Union Navy to gunboat duty in the waterways of the rebellious Confederate States of America.

Nyanza, a wooden side wheel steamer built at Belle Vernon, Pennsylvania, in 1863, was purchased by the Navy at Cincinnati, Ohio, 4 November 1863; and commissioned at Mound City, Illinois, Acting Lt. Samuel B. Washburn in command 21 December 1863.

During the Civil War, Nyanza patrolled the Mississippi River and its tributaries protecting Union lines of communication and supply on the great inland waterway and preventing Confederate activity.

After hostilities ceased, Nyanza decommissioned at New Orleans, Louisiana on 21 July 1865 and was sold at public auction to Owen Finnegan 12 August 1865.