Leaves Floating Downstream
When daylight shortens in our deciduous temperate forests, leaves begin to fall. Many leaves are blown into or fall directly into headwater streams and these flow into and through the whole system. They bunch up at pinch points like boulders, cobbles, pool bottoms, and against logs or other woody material. These bundles of leaves are known as leaf packs, and they provide an invaluable food source to the bacteria and aquatic insects that live in the stream. These creatures wait all year for the autumn leaf fall and quickly get to work to break down the leaves and stems into fine particles of organic matter.
Learn more about stream ecology here - https://www.ausableriver.org