Waterway Site Observation and Testing

Using a Secchi DiskDissolved Oxygen (DO) & Temperature Profiles – Dissolved oxygen is the most critical indicator of a lake’s health and water quality. Dissolved oxygen levels in natural waters are dependent on the physical, chemical and biochemical activities prevailing in the water body.

Oxygen is added to aquatic ecosystems by aquatic plants and algae through the process of photosynthesis and also by diffusion at the water’s surface and atmosphere interface. Primarily, animal, plant and bacteria respiration deplete oxygen. Oxygen is required for fast oxidation of organic wastes including bottom muck. When the oxygen is used up in the bottom of the lake, anaerobic bacteria continue to breakdown organic materials, creating toxic gasses such as hydrogen sulfide, in the process.

For a healthy game-fish population, oxygen levels in the 6-10 mg/L range are necessary. Respiration stress in most fish occurs when oxygen levels are reduced below 4-5 mg/L.

Temperature must also be considered when looking at oxygen levels in lakes since warmer water cannot hold as much oxygen as cooler water. A difference of 1˚C or more between surface temperature and temperature at depth indicates that the lake is stratified, and is therefore in danger of having low oxygen levels below the surface.

Secchi Disk – Secchi depth is a mechanical test to judge water clarity. It is accomplished by lowering a black and white disk into the water and recording the point at which it can no longer be seen. Higher values of Secchi disk depth indicate greater water clarity. Generally, nutrient rich lakes tend to have Secchi depths less than 9 feet and highly enriched sites less than 3 feet. However, many lakes are exceptions to this rule based on other parameters, and Secchi disk depth in isolation cannot be used to diagnose a lake's overall health.

Visual Algae Identification – Algae comes in different colors and some species produce toxins and/or odor compounds, so the first step in identifying it is to see it in its natural state. If the type or quantity is a problem, further tests will be conducted in the lab.

Aquatic Plant Identification – Different plants respond differently to herbicides, so identification of problem plants is absolutely necessary before treatment and many are easily identified in the field.