Nitrate Runoff
Nitrate Runoff is when rain washes plant food from soil into streams and lakes.
Think of it this way
Set a tilted cutting board in the sink and sprinkle salt across it. Pour water from the top and watch the salt wash down the board into the sink below. Nitrate runoff works the same way. Rain flows over soil that holds fertilizer, picks up the nitrates, and carries them downhill into streams and lakes.
Explaining nitrate runoff by grade level
When you put too much plant food on dirt, rain washes it away. The rain picks it up and takes it to a pond or stream. Fish and frogs live in that water. Too much plant food in the water can make them sick.