A Secchi Disk is a simple way to measure turbidity. The Secchi disk is lowered into the water until it is no longer visible, and that depth is measured. Secchi depth values that are high indicate clearer water, and low Secchi depths indicate high turbidity.
Turbidity is the measure of suspended solids in the water. When the water is clear, there is low turbidity; when the water is cloudy, there is high turbidity, which allows less light to penetrate through the water. Light is required for seabed grasses to flourish.
What causes high turbidity? Run-off from the land due to stormwater, shore-line erosion, excessive algal blooms, and pollution all contribute to high turbidity levels.