Degraded Habitat Expand For many fish species, the smaller rivers and streams of a catchment are vital for spawning and juvenile habitat. The state of the tributaries and the quality of the water flowing out of them also has a direct influence on the flora and fauna that inhabit the main river. During our surveys of the upper Wye in the mid 1990s we found the habitat of nearly all the tributaries was in a poor state. We found a similar situation a few years later when we came to the Usk and other parts of the Wye catchment. How and why habitat degradation happens. What the Foundation does to restore habitat in streams and rivers.