A stormwater gully comprises a chamber in which an outlet assembly is installed. The outlet assembly comprises filter units connected to an outlet housing. In use, stormwater can flow from the chamber in an upwards direction through filter units into the outlet housing. The outlet housing has an outlet, which extends from the gully. At high rates of flow, the water level in the chamber will rise until water can flow into the outlet housing through bypass inlets. The bypass inlets are connected to the interior of the housing by siphons defined by arched regions of a top cover. The siphons allow rapid discharge of water until the water level returns below the level of the bypass inlets. A slow drain down feature is provided which enables the chamber and outlet assembly to be drained below the level of the primary inlet.