These medium to large rivers in tropical, subtropical and temperate lowlands have markedly seasonal flows due to seasonal water supply in the catchments. Their single or multi-channelled forms link to floodplain wetlands, and transport large floods during wet seasons: summer in the tropics or winter-spring in temperate latitudes. Productivity is high, both within channels and on connected floodplains, with algae and aquatic plants supporting complex food webs, and providing seasonal nurseries for breeding animals.