Often humans will seek to improve the habitat of trout in a stream by providing some kind of structure under the water. People will sometimes dump anything in the stream, think that the fish will want to take shelter in it. Car bumpers, shopping carts, dog houses. Generally fish prefer the smooth curves of nature to the hard edges of humans. But more importantly, if the structure is not proper and is not put in the right place in the stream, the flow of the current might find an erodible bank and so cause more harm than good.
