This report describes a risk assessment of the alien species Australian swamp stonecrop (Crassula helmsii) (hereafter: Stonecrop) in Europe. The species is native to Australia and New Zealand but has been imported in many places in the world as ornamental species for aquaria and garden ponds. It is a small perennial species of water bodies and wetlands. The species is considered invasive in several European countries. The present risk assessment is based on a detailed risk inventory and supports national and international decision making on the management of Stonecrop. The available information and data were analysed and the risks were classified by a team of experts using the Harmonia+ protocol.