Abstract: A floating weir assembly for controlling the discharge of fluid from a fluid reservoir. The weir assembly includes a buoyant body preferably comprising a sidewall surrounding a central bottom opening. A weir is provided on the inside surface of the sidewall, and a gauge is provided on the opposite side of the sidewall's inside surface. The sidewall may provide a ballast chamber for holding ballast, such as sand. By adjusting the amount of the ballast, the depth to which the body is submerged can be varied. By distributing the sand circumferentially, the body can be leveled in the fluid to ensure accuracy of the weir. Because the sidewall is partially submerged, undesirable surface matter, such as oil and debris, is prevented from entering the weir. While there are many applications for this floating weir assembly, a preferred application is in the field of sewage treatment systems.