It is a black and white wood, plastic or metal disk about 8 inches in diameter that is lowered into the water being tested until it disappears. The depth at which it can no longer be seen is called the secchi depth. Experiments have shown that sufficient light to support plant growth penetrates to approximately 2.5 times the secchi depth. Another important measurement related to transparency and algal growth is the chlorophyll content of the water sample. Chlorophyll is the green plant pigment responsible for capturing the sun's energy in the process of photosynthesis.
Algal blooms can greatly reduce water clarity under certain conditions.
The chlorophyll content is related to the abundance of phytoplankton, minute free-floating aquatic plants, in a water sample. The amount of solids present in water is a consideration in its suitability for domestic use. Waters with total solids content of less than 500 ppm are most desirable with standards generally recommending an upper limit of 1000 ppm for potable water. Waters with a high solids content often have a laxative effect on people whose bodies have not adjusted to them. Sufficient nutrients are present in Higginsville City Lake to support plant growth that would turn waters green however turbidity due to suspended sediment turns waters brown and limits the light available for plant growth.