Riparian and floodplain corridors are particularly biodiverse and often form key habitat for animals in the terrestrial landscape, and in most parts of the world they support more species of plants and animals than any other landscape unit. Rivers are nature's natural corridors. The flow of water, nutrients and sediments, and the movement of species along streams, generates diverse habitat in riparian and floodplain corridors across terrestrial landscapes. Connectivity is one of the fundamental attributes necessary for ecological integrity of aquatic ecosystems and particularly for rivers. Longitudinal, lateral and vertical connectivity allow for natural ecosystem processes and functions to occur such as the natural periodicity and magnitude of water flows, associated thermal regimes and sediment and nutrient transport, and movement of species through the riverscape. In certain parts of the world there are policies and efforts intended to protect stretches of river that maintain a high level of connectivity and other aspects of ecological integrity.