Why do we sometimes leave debris in the river, or add debris to the river?
Woody debris has lots of benefits, both to the river and the wildlife that lives in it. Leaving it where it falls, or even adding it artificially, is a great idea, as long as there’s no risk it could cause flooding or erosion.
Historically all wood that had fallen into watercourses was removed, because it might look unsightly, or because of the risk of it causing flooding or erosion. However, it’s much better to consider each piece individually – often the advantages of leaving it where it is outweigh the risks.
Woody debris provides habitat for fish and insects, can help reduce erosion of river banks and creates more variety in the flow and the depth of the river. It’s so valuable that we sometimes create it artificially in well-chosen locations, to improve the flow in rivers which have become too wide.
Improving the health of a river doesn’t just help things at the bottom of the food chain. The benefits are passed on to larger fish, and to the top predator in our rivers, the otter, which is making a comeback after decades of decline.