Utah Standards

Maximum temperature for warmwater fish is 27 degrees C
Maximum temperature for coldwater fish is 20 degrees C

The temperature of water is a measure of how much heat energy the water contains. In the U.S. we usually use the Fahrenheit scale to measure temperature. On this scale water freezes at 32 degrees and boils at 212 degrees. However, scientists usually use the Centigrade (or Celsius) scale. Water freezes at 0 degrees C and boils at 100 degrees C.

Converting Celsius to Fahrenheit
Converting Fahrenheit to Celsius
°F = [(9/5) x °C] + 32  °C = (5/9) x (°F-32)

Natural factors that influence temperature: Human factors that influence temperature:
  • Geographic area - waterways reflect the surrounding climate. If the climate is warm all year, the water is generally warm. Waterways in colder climates tend to change more throughout the year.
  • Seasons - air temperature affects water temperature. During the winter water may freeze and during the summer the water may be warm.
  • Sources of water - waterways fed by snow melt will be cold during the spring and summer. Waterways fed by hot springs may keep water warm throughout the year.
  • Channel shape - Because stream water heats up from the sun and from contact with the warmer earth, a narrow, deep stream will be cooler than a wide, shallow stream, if all other factors are equal.
  • Riparian shading - Streams that receive shade from riparian vegetation may have cooler temperatures than those that are exposed to more sunlight.

  • Removal of riparian vegetation - when vegetation is removed along waterways there is less shade and the water heats up faster.
  • Activities that cause a stream to become shallower and wider - deep, narrow channels stay cooler than shallow, wide channels.
  • Type of substrate - waterways with plants at the bottom absorb more heat than waterways with a concrete bottom and are therefore cooler.
  • Discharge from industries - industries like power plants may discharge warm water into waterways.


Why care about temperature?

Water temperature greatly affects macroinvertebrates and other aquatic organisms. Macroinvertebrates, fish and amphibians are cold-blooded. The metabolisms of these animals are affected by temperature. It speeds up and slows down based on the surrounding temperature. If the temperature changes too drastically, their metabolisms may not function as well, decreasing their ability to reproduce and survive. Optimal temperature ranges for organisms vary. Trout do best at temperatures below 22°C while carp may do fine in temperatures as high as 28°C. Fish can be divided into two groups, coldwater fish (who require fairly cool temperatures) and warmwater fish (who can survive in warmer water temperatures).