Water that is free from pollutants is colourless and odourless. A stream should be ideally surrounded by vegetation (plants). Plants give shade and keep water cool. Rocks, gravel and sand should be present in and around the stream. Some animals hide from predators between rocks. Water should flow continuously to prevent bacteria growing and causing bad smell. Many different plants and animals around the water indicate a healthy stream. This supports the food chains in the habitat. The presence of many different plants, animals and micro organisms indicate a good biodiversity in an area.