In February 2019, marine biologists feared for the safety of the Great Barrier Reef off the coast of Queensland, a state in Australia, after it was inundated with polluted floodwater. If contaminated floodwater enters the ocean it can affect water quality and disrupt delicate ecosystems, such as coral reefs. Floods Carry Contamination Floodwater can be contaminated with pollutants such as agricultural pesticides, industrial chemicals, debris, and sewage. Erosion and sedimentation have a more negative impact on ecosystems that are already degraded or heavily modified. Suspended sediment eventually settles out of the water in a process called sedimentation, which can clog riverbeds and streams, smother aquatic organisms, and destroy habitats. As floodwater carries material from the eroded banks, it suspends sediment in the water, which can degrade water quality and lead to harmful blooms of algae. For example, fish can be displaced and their nests destroyed.įloods Cause Sedimentation and Erosion Floodwater can also alter the landscape, for instance, by eroding riverbanks and causing them to collapse. Unpredictable floods can be harmful even to aquatic life. In 2012, hundreds of animals, including many vulnerable one-horned rhinos ( Rhinoceros unicornis), were killed in floods that swamped Kaziranga National Park in the Indian state of Assam. Floods Can Harm Wildlife Flooding can have a negative effect on wildlife, causing drowning, disease proliferation, and habitat destruction. In fact, some ecosystems rely on seasonal flooding to drive ecological processes. The human cost of flooding can be large, but events like this have a big impact on the natural world too, and the effects are not always negative. The aftermath was devastating deadly waterborne diseases like dysentery and cholera spread quickly, and those who survived faced the threat of starvation. The Yangtze and Huai Rivers broke their banks, killing as many as several million people. The Central China flood of 1931, for example, was one of the worst flooding events in recorded history.

Flooding is one of the most common types of natural disaster, and the results are often fatal. When rivers flood, the effects can be catastrophic. While water is essential to life, it can be a destructive force too. It is hardly surprising that rivers have been an important part of human history: They provide food, freshwater, and fertile land for growing crops.

Dordogne river floods