That's because these microscopic plants consume oxygen at night, taking it away from fish, insects and crustaceans . Slippery, slimy algae can also be a nuisance if you like to swim in the lake. Oxygen dissolved in water is essential because aquatic plants and animals need dissolved oxygen to live. Cold water can hold more oxygen than warm water because gases are more easily dissolved in cold water. Some of the oxygen dissolved in water comes directly from the atmosphere.
Oxygen enters the water more readily when mixing occurs, as in waves on the lake's surface.
Algae and plants that live in the water also produce oxygen during daylight hours through photosynthesis . Some fish, like trout, are very sensitive to changes in water quality. If the lake doesn't have enough dissolved oxygen, or if the water is too warm, trout will die. Other fish, such as carp and catfish, flourish in warmer temperatures and can tolerate lower dissolved oxygen. If your lake has many trout, then it is probably very healthy.