All the water that flows in streams has to come from somewhere. We know that water in big streams comes from littler streams that flow into it—tributaries to the stream. But how does water get into those little creeks and brooks? All of this water comes from the sky, mostly in the form of rain and snow. When it rains, some water flows over the ground, eventually joining a stream. Much more of the rainwater seeps down into the soil, moving slowly underground until it, too, finds a stream or lake to join. When snow, sleet, hail and ice melt, the meltwater does the same thing. Pour out a bucket of water in your yard, street, or driveway. What happens to that water? Where does it go? How do you think it gets to the nearest stream?
As this water flows across the land, the land can change it. If the water flows across chemicals, such as automobile oil from roads or pesticides from farms, those chemicals become a part of the water. If the water flows across bare soil on construction sites and becomes muddy, the water carries the soil particles, called sediment, with it. The water also picks up other oils, fertilizers, and other chemicals that can damage fish. These chemicals and sediment eventually join the stream when the water does, and that can affect the trout. (photo courtesy of USDA NRCS)