During the day, the hair-like strands of green algae produce relatively large volumes of dissolved oxygen. At night, the metabolic processes reverse and the masses of green algae consume oxygen and produce carbon dioxide gas as a cellular respiratory waste product. The rapid creation of carbon dioxide in the water can change the pH level too quickly for aquatic organisms, such as fish, resulting in stress, and abnormal behaviors that make them much more susceptible to predators. During winter months in temperate regions the algal mats die and decompose, creating a significant biological oxygen demand due to bacteria feeding on the decaying organic plant matter. Severe competition for limited oxygen resources often results in a phenomenon referred to as winterkill, a large die-off of fish populations that remains generally undiscovered until the following spring.