Understanding and classifying the raw water transfer invasion pathway

Raw Water Transfer (RWT) schemes move large volumes of freshwater between separate waterbodies to supply water as a specific commodity. Water is translocated by complex purpose-built networks of pipelines, tunnels and water supply canals. RWTs form hydrological connections between waterbodies across various spatial scales, and create a pathway of introduction and spread for a diverse range of invasive non-native species (INNS). Though occurring globally in large numbers, RWTs are not currently well represented by the standard pathway classification framework adopted by the Convention on Biodiversity (CBD). At present, RWTs are included within the ‘corridor’ category, which denotes the natural spread of organisms to neighbouring regions through transport infrastructure i.e. navigable canals/artificial waterways. However, RWTs are not routes for vehicle transport, and species are translocated between often non-adjoining waterbodies by the intentional transfer of water, not via natural spread. We provide a background for the complex RWT pathway and evidence of INNS spread through RWT schemes globally, and explore several options for improved RWT classification within the CBD framework—we recommend that the current corridor category is modified slightly to accommodate the addition of RWTs as a distinct sub-category, as separate from a clearly defined ‘navigable canal/artificial waterways’ sub-category. Accurate classification will increase understanding and awareness of this high-risk pathway, and support much-needed insight into its distinct stakeholders and drivers. Further, delineating RWTs from navigable canals/artificial waterways will help to identify widespread opportunities for pathway management and policy development, in addition to supporting more accurate future assessments of the risks and economic costs of the corridor pathway category.