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    Water temperature is measured as the degree or intensity of thermal energy in water. In the U.S., we usually use the Fahrenheit scale to measure temperature - where water freezes at 32 degrees and boils at 212 degrees; however, scientists usually use the Centigrade (or Celsius) scale - where water freezes at 0 degrees and boils at 100 degrees.


    Water has very high freezing and boiling points compared to other similar molecules. Likewise, the heat required to melt or evaporate water is higher than similar sized molecules. As a result, at Earth’s temperatures, water is present as a liquid, but also as a gas (water vapor) and as a solid (ice).  Also, Earth doesn’t experience huge and rapid changes in temperature. Our planet is sometimes called the “goldilocks” planet – not too hot for all the water to evaporate away and not too cold for all the water to freeze.


    Dead Fish

    Since many aquatic organisms are cold-blooded, their metabolism speeds up and slows down with the animal's surrounding temperature. Not all organisms thrive at the same temperature because they have adapted to their optimal temperatures. Extreme changes in temperature affect how well fish can eat, reproduce, and even breathe - as temperature will change levels of dissolved oxygen.

    Many chemical and biological reactions have optimal temperature ranges.  Water quality criteria attempt to bracket appropriate temperatures to protect “cold water” fish and “warm water” fish. Most temperature related water quality problems come from water that has gotten too warm. Increased temperatures may result from hot discharges from industry and increased exposure to the sun from loss of shading or river beds that become more shallow and wider.  Increased air temperatures predicted from global climate change will also result in higher water temperatures.

    Utah Standards

    • Maximum temperature for warmwater fish is 27°C
    • Maximum temperature for coldwater fish is 20°C


    • Geographic area - waterways reflect the surrounding climate. Therefore, if the climate is warm all year, the water is generally warm; on the other hand, waterways in colder climates tend to change more throughout the year.
    • Seasons - air temperature affects water temperature. During the winter, water may freeze. In contrast, the water may be warm during the summer.
    • Sources of water - waterways fed by snowmelt will be cold during the spring and summer, while 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.

    Channel Shape


    • Removal of riparian vegetation - when vegetation is removed along waterways, less shade is available 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.
    • Learn more about limiting human impacts: Protect Your Water.


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

    Utah Water Watch- Learn how volunteers across the state monitor temperature.

    Stream Side Science- Explore different lesson plans involving water temperature and see how they apply to the different core curriculums for grades k-12.