This is water that flows off the land. It may come from rain, snow or ice. Runoff can also arise when people apply too much water somewhere, such as on a farm field or lawn. Water may run off soil because the soil is too soaked to hold more. Or it might run off of a paved road or driveway because it can’t penetrate the hard surface. Runoff eventually ends up in streams, ponds, rivers, lakes and oceans. Before it gets there, the water can pick up dirt, pollutants and even medicines. All of those substances can end up in the waterways where the runoff pours in and may cause problems for creatures living within them.
In a sentence
The ditches farmers use to drain their fields may also carry runoff full of pollutants.