These thresholds are determined via water quality standards . Other pollutants Low Dissolved Oxygen Dissolved oxygen is a basic requirement for an healthy aquatic ecosystem. Larvae and juvenile fish are more sensitive, requiring even higher concentrations of dissolved oxygen. Many fish and other aquatic organisms can recover from short periods of low dissolved-oxygen availability. Prolonged exposure to low dissolved oxygen conditions can suffocate adult fish or reduce their reproductive survival by suffocating sensitive eggs and larvae.
Fish can starve when aquatic insect larvae and other prey die in response to the altered conditions.
Although oxygen concentrations fluctuate under natural conditions, severe oxygen depletion usually results from human activities. Introducing large quantities of biodegradable organic materials, plant, fish, or animal matter, into surface waters can rapidly consume available oxygen. Leaves, lawn clippings, sewage, manure, milk solids, and other food processing wastes are examples of oxygen-depleting organic materials that enter our surface waters. Pollution containing organic wastes provides a continuous supply of food for the bacteria, which accelerates bacterial activity and bacterial population growth. In polluted waters, bacterial consumption of oxygen can rapidly outpace oxygen replenishment from the atmosphere and photosynthesis performed by algae and aquatic plants.