On sunny days, mats of tangled Spirogyra usually float on the surface of the water, kept afloat by tiny bubbles of oxygen created through photosynthesis. The algal mats sink when the sun goes down and the process reverses as the level of photosynthesis diminishes. Subsequently, the algal strands consume oxygen for cellular respiration and produce carbon dioxide as a waste product. In highly fertile areas, thick algal mats may cause large fluctuations in the dissolved carbon dioxide and oxygen content of the water body. The resulting changes in the water's pH can occur rapidly, leading to stress and even death of other organisms present in the environment.