International Day of Action for Rivers 2026 - River Complexity

When looking at healthy river systems, complexity is very important. Having different sections to a river will provide different habitat and functions. Here are some complexities that we look for in rivers:

Riffles: The shallowest part where water is usually running over rocks. This is where water is the fastest and there is the most oxygen. Sometimes fish will wait downstream from riffles to wait for food to flow their way.

Runs: This is when water flows at a more uniform pace and is usually a deeper part of the river.

Pools: These are along the curves and meanders of rivers. They are created when fast moving water breaks away the sediment of the water banks. This is where the water slows down and wildlife like fish and invertebrates can take a break from the fast flowing water.

Riparian vegetation: Vegetation along the water will help with bank stabilization, filtering out pollutants and sediments in the water, while also providing temperature refuges.

Channelization prevents a lot of this complexity in rivers that can make it hard for wildlife to thrive. Many projects have been happening in the region to re-naturalize rivers to make them more complex and bring the rivers back to how they once were.