Or send an email with your name, address, and phone number. We hear the sounds the water makes as it runs over rocks, we feel its coolness when we dip our hand, and while it is no longer a recommended activity, we once tasted it when we slaked our thirst.
Many modern rivers are identifiable by their odors.
Perhaps most of all, we experience a stream with our eyes, watching the play of sunlight on its surface or a fish taking a fly. What we can't see, at least without the help of a good microscope, is the teeming world of tiny organisms that sustain the stream's life and health. It is as if we were to go to New York and marvel at the huge buildings, while the millions of people who are the lifeblood of the city remain invisible. Yet as many as a billion bacteria, plus millions of protozoa and hundreds of thousands of diatoms, occupy a square centimeter of a streambed, and the collective efforts of such microorganisms provide or process most of the energy that supports the visible life of the stream. Almost all the biologically useful energy on Earth comes from plant life.