Abstract: Described is a preferred fluid flow diverter, such as a rainwater diverter, having an outer duct, and an inner duct within said outer duct and defining a reservoir to collect fluid. The diverter also includes a drainage duct extending from the reservoir to the exterior of the outer duct. The inner duct has a bypass opening at a height above the drainage duct. In this manner, fluid flowing into the inner duct is diverted through the drainage duct, and excess fluid unable to flow through the drainage duct (e.g. during heavy rains) accumulates in the inner duct to the height of the bypass opening and then excess fluid not retainable by the reservoir flows through the bypass opening and is exhausted through the outer duct. Also described are a rainwater diversion apparatus and method incorporating the preferred fluid flow diverter.