1 . Rivers are very important. Humans rely on them for food and water. But rivers can destroy things, too. They can flood, or rise over their banks, making the water run into the nearby land. Floods can also kill humans and wildlife. However, floods are not always bad. Some ecosystems need them every once in a while.

Flooding can not only harm animals but also destroy habitats. For example, a flood in Australia in 2022 caused massive animal habitat loss. Flood waters can pick up dirt (泥土) from riverbanks, which makes the water dirty. Too much dirt will clog rivers and streams, preventing the river from flowing. Sometimes flood waters can carry pollution to the sea and harm marine life. In addition, flood waters can carry disease, including hepatitis A (甲肝) and cholera (霍乱) .

However, not everything about floods is bad. Sometimes they bring new life to ecosystems. Flood waters carry nutrients to the nearby land. Over time, the water dries up and leaves behind particles (微粒) of dirt and mud. The particles are called sediment (沉淀物) which can be good due to its ability to improve the dirt and helps plants grow. Floods are important to some animals as well. For instance, some animals see floods as a sign that it is time to mate or migrate. Floods leave sediment on river beds where baby fish can grow and carry nutrients for small animals in the water to eat. Moreover, in dry seasons, water might dry up, but floods help refill the wetlands, keeping the ecosystem going.

Floods are a part of nature. They can destroy living things and the environment. But some ecosystems need floods to survive.