A dammed stream refers to a series of pooled areas of stream that are linked together by cascades or waterfalls to allow the stream to keep running through each pool and into the next one. The benefit of this arrangement is that if your pump doesn't work properly, then you can be reassured that each pool can operate independently until the pump is mended. The whole effect is very pleasing to the eye but you will need a large garden or yard space to accommodate a dammed stream.