While many people may believe that what makes a stream clean is how clear the water is that's not the only factor. There are many separate factors that make a stream clean other than how clear the water is. Here is an example of a clean stream. As you can see the stream has a wide variance of different creatures a neutral PH and the water is clear. Additionally there are many creatures with a PT level of one meaning they are intolerant to pollution this means that if the stream was polluted they wouldn't be able to live there. Another thing about the stream that signals that it is clean is probably the most obvious "Was there any pipes leading into the river" for this stream no. But if there ever is odds are the stream isn't clean. Remember, if you find a stream near you isn't clean do your best to clean it. For example, get a group of your friends or people who are concerned for the stream as you are and clean the stream. Sometimes, a little bit can go a long way for the health of a stream always do your best to make it better for the next generation.