USS Niagara, commonly called the Brig Niagara or the Flagship Niagara, is a wooden-hulled snow-brig[b] that served as the relief flagship for Oliver Hazard Perry in the Battle of Lake Erie during the War of 1812. As the ship is certified for sail training by the United States Coast Guard, she is also designated SSV Niagara. Niagara is usually docked behind the Erie Maritime Museum in downtown Erie in the U.S. state of Pennsylvania as an outdoor exhibit for the museum. She also often travels the Great Lakes during the summer, serving as an ambassador of Pennsylvania when not docked. It was listed on the National Register of Historic Places in 1973 and was designated the official state ship of Pennsylvania by the Pennsylvania General Assembly in 1988.

In sailing, a snow, snaw or snauw is a square-rigged vessel with two masts, complemented by a snow- or trysail-mast stepped immediately abaft (behind) the main mast.