Zizania latifolia is already established in Belarus, Belgium, France, Lithuania, Russia, and Ukraine. In addition, there are a smaller number of persistent planted populations from Estonia, Germany, Ireland, Switzerland and the United Kingdom. 

The overall likelihood of further entry of Z. latifolia into the EPPO region is moderate with a moderate uncertainty. 

The likelihood of establishment outdoors is very high with low uncertainty. Habitats are widespread within the EPPO region and further establishment is likely in regions where habitats and climatic conditions are conducive for growth. Likelihood of establishment in protected conditions is very low with moderate uncertainty. 

The potential for spread within the EPPO region is high with a moderate uncertainty. Z. latifolia can spread naturally via plant fragments in waterways, and via human assisted spread (e.g. horticulture trade, fragmentation due to management practices). 

The magnitude of impact in the current area of distribution (excluding the EPPO region) is very high with a moderate uncertainty. Z. latifolia has negative impacts on biodiversity and ecosystem services. Persistent populations can act as ecosystem transformers, favouring wetlands draining, eutrophication and sedimentation. The plant has also been shown to have socio-economic impacts on low-lying agricultural land and associated drainage systems. The EWG considered that the potential impact in the EPPO region is high with a high uncertainty. Similar types of impacts are expected though the high rating reflects the potential impacts on biodiversity and ecosystem services in the EPPO region. A high uncertainty reflects the limited amount of scientific evidence on the negative impacts and the perceived early stage of the invasion in the EPPO region. 

Based on high likelihood of spread (moderate uncertainty) from existing established populations in the EPPO region, and high impact (high uncertainty) the overall risk appears correct.