U.S. Environmental Protection Agency


Date of this Version



Journal (Water Pollution Control Federation), Vol. 42, No. 5, Part 1 (May, 1970), pp. 824-828


U.S. government work


Water temperatures affect aquatic organisms in a number of ways, both directly and indirectly. Some of the latter effects are quite subtle. High temperatures can have direct lethal effects but sublethal levels operating over long periods can be just as harmful through delayed lethal effects and the production of nonlethal stresses which eventually result in changes in the population, reduced growth or reproduction, and the lowering of resistance to parasites, dis ease, and competitors. Temperature, in combination with certain other factors such as day length, influences re producing processes. High water temperatures may stimulate or retard migration, spawning, feeding, and growth, may influence enzyme and hormone activities and other physiological processes, and may speed up the action of toxicants.