What is the connection between organisms in a stream and the dissolved oxygen level?

Organisms in streams need oxygen to live when lacking dissolved oxygen it will kill these organisms. edit: unless the organisms in the stream are photosynthetic, in which case they will increase the oxygen levels. however, by far, most organisms in a stream are not photosynthetic and oxygenation occurs solely through aeration and surface area dissolving from the air. so, to answer the question, organisms (most organisms which aren't plant-based photosynthetic organisms) decrease the amount of oxygen in a stream. edit: a flowing stream has turbulence which helps aerate the water, increasing dissolved oxygen. In contrast, stagnant water tends to be low in dissolved oxygen, except near the surface. Multicellular animals (like fish) need a good supply of dissolved oxygen to thrive.