Used to measure the transparency of water, a secchi disk is a round piece of wood painted black and white.
Monitors lower the secchi into the water until it disappears from view.
That depth is an indirect measure of the amount of suspended particles, such as algae, microscopic organisms and soil, in the water. In the New Hampshire Seacoast Region, the Great Bay Coast Watch will be participating in the Dip-In. The information it gathers is kept in a database at UNH's Jackson Estuarine Laboratory. Ann Reid, Watch coordinator, and other experts train the volunteers in water monitoring techniques. The Watch has found that the waters of Great Bay are generally in good shape.