text: what makes stream water so clear in the fall?   that's not always the case.... the clearness of the water is also due to whatever solids are suspended in the water.  that's called turbidity.  granted, there are indeed instances where algae will grow at an astonishing rate, but streams don't tend to have overwhelming populations of algae, that in eutrophic lakes.  take a look at the water on a summer day, on a spring day, heck even a winter day.  i'm betting the difference will be  minimal, but don't get me wrong, heat and sunlight does play a role in water clarity.