Any water moving across the land is a stream. We usually use the word “river” for bigger streams and “brook” or “creek” for smaller streams. Trout often prefer smaller streams, where the water is fast-moving and cold. Trout are usually happiest when the substrate, or stream-bottom material, is rocky, such as gravel, boulders or something in between. A healthy stream meanders, which means that it curves across the land instead of just flowing straight. And a healthy stream also has riffles and pools. Riffles are the rockier, bubbly parts of streams where water can sometimes look white. Pools are deeper, smoother parts of the stream that can be a good place for trout to rest.  (photo courtesy of NYC DEP)