Because there is a limited supply of oxygen in the water, an increase in decaying organic matter decreases the oxygen supply. Aquatic life populations are thus deprived of necessary oxygen levels and cannot survive. Excess decaying organic matter also blocks surface light for plants, causes odor and surface scum, and clogs water systems. Sources of excess organic matter are materials such as sewage from farm runoff, waste treatment plants, canneries, livestock feedlots, sanitary landfills, excess fertilizers, and grass and leaves dumped into gutters or streams. Toxic elements injure the growth or metabolism of an organism.
Toxins can poison aquatic life, destroy their food supply, and deform fish larvae.
May be in a stick, rock, or leaf case with its head sticking out. May have fluffy gill tufts on lower half. Tails may be webbed together. Walks slowly under water. Does not swim on surface.