Dissolved Oxygen & Water Temperatures

Dissolved Oxygen Meter

Dissolved Oxygen Meter

In 2008 the Lake Shamineau Association purchased equipment for measuring dissolved oxygen and water temperatures. The Water Quality Committee has been regularly collecting data since then.

The importance of Dissolved Oxygen (DO)

Dissolved Oxygen (DO) is found in microscopic bubbles of oxygen that are mixed in the water and occur between water molecules. DO is an important indicator of a lake’s ability to support aquatic life. Fish breathe by absorbing dissolved oxygen through their gills. Oxygen enters the water by absorption directly from the atmosphere or by aquatic plant and algae photosynthesis. Oxygen is removed from the water by respiration and decomposition of organic matter.


Measurement of Dissolved Oxygen

Dissolved Oxygen can be measured with an electrode and meter or with field test kits. The amount of oxygen dissolved in water is expressed as a concentration, in milligrams per liter (mg/l) of water.

Dissolved oxygen levels are also often reported in percent saturation. The saturation level is the maximum concentration of dissolved oxygen that would be present in water at a specific temperature. Percent saturation is calculated by dividing the measured dissolved oxygen concentration by the saturation level and multiplying by 100.

Factors that affect Dissolved Oxygen

  •  Volume and velocity of water flowing in the water body
  • Climate/Season
  • The type and number of organisms in the water body
  • Altitude
  • Dissolved or suspended solids
  • Amount of nutrients in the water
  • Organic Wastes
  • Riparian Vegetation
  • Groundwater inflow

Water Temperature/Thermo cline

Water temperature has an important influence upon the activities of all fish. Fish are cold-blooded and their bodies are always the temperature of the surrounding water. During the winter, colder water slows down their metabolism, so they need about a fourth as much food as they consume in the summer.

Most fish don’t spawn unless the water temperature is within rather narrow limits. Bass and other fish eventually die out when stocked in lakes that remain too cold during the summer. While some fish have a wider temperature tolerance than others, each has a certain range within which it tries to stay. Schooling fish suspended over deep water lie at the level that provides this temperature.

The temperature in a lake is seldom the same from the surface to the bottom. Usually there is a warm layer of water and a cooler layer. Where these layers meet is called a thermocline. The depth and thickness of the thermocline can vary with the season or time of day. This is important because many species of game fish like to suspend in, just above, or just below the thermocline. Many times baitfish will be above the thermocline while larger game fish will suspend in or just below it.

Thermocline (sometimes metalimnion) = a layer within a body of water or air where the temperature changes rapidly with depth.