Temperature of water is one of its most basic properties, and many other parameters depend on temperature for accuracy. With temperature data, we can monitor thermal loading or discharge and determine changes in the thermocline, which affect the health of aquatic species and organisms. Many aquatic organisms are sensitive to high temperatures. The solubility of oxygen is lower in warmer water, thus limiting oxygen supply.

YSI measures temperature with a high-precision thermistor sensor. The resistance of the thermistor changes with temperature. The measured resistance is converted to temperature using an algorithm.