National Weather Service United States Department of Commerce

Date Posted: March 15, 2016

top Back to blog

It looks like some of the water from yesterday’s rain showers made it to this river! When it rains on a mountain, the water flows to the bottom and collects towards the base.  But what happens if there is too much water? Water rises over the river bank and spreads out -- that’s called river flooding. Flooding usually happens over days or weeks, but sometimes the water rises quickly, in just a few hours. That’s called a flash flood. And we know it’s important to never walk or drive through floodwaters! You can learn more about flood safety at or with a video at

Even when it doesn’t flood, as rainwater moves over the ground it can pick up natural and human-made pollution. Because all rivers lead to our one ocean, they can carry pollution all the way from mountains -- or your backyard -- to the sea. Find out more about becoming an ocean guardian and protecting your rivers, mountains, and the ocean here: