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In addition to being required by aquatic organisms for respiration , oxygen is necessary to help decompose organic matter in the water and bottom sediments . Atomic oxygen is present in the earth 's atmosphere at altitudes where satellites typically orbit . As the water temperature rises , a fish , being a cold-blooded animal , experiences a rise in its metabolic rate , increasing its need for oxygen at the same time less oxygen is available . When dissolved oxygen is present in the feed-water , an attack of the feed-water line , heaters and economizer can be expected with the severity of the problem dependent on the concentration of the dissolved oxygen and the temperature involved . Oxygen is necessary for many forms of life on Earth , so any compound that can help detect its presence is bound to be useful . Water containing the methylene blue indicator is blue when oxygen is present . Hence carbon is tetravalent , nitrogen is trivalent , oxygen is divalent , and so on . Dissolved oxygen is necessary for healthy lakes , rivers , and estuaries . Scientists have generally thought that oxygen was scarce in Earth ’ s atmosphere until about 2.4 billion years ago . Anoxic - A condition where no oxygen is present . As long as free oxygen is present inside the plastic , the hydride will react quickly with the oxygen .