There are two ways to measure the Secchi depth, depending on how close you are to the water.

They are known as the direct and the indirect method. The direct method applies when you can easily reach the sea surface e.g. in some boats or pontoons. The indirect method applies when you are on a jetty, or other position from which it is not easy to reach the waters’ surface (see drawing below).

Reference point

You should measure the Secchi depth from the same distance above the water each time. The point you measure from is the reference point. This could be the jetty railing if using the indirect method, or the water’s surface if using the direct method. Only measure from the waters’ surface if it is safe to do so. Don’t want to lean over to reach the water and risk the chance of falling in.