Here they are. Also, permission may be needed to perform any tests on a pond so you may have to look into that. It is very frustrating to have to re-do activities because of public abuse of property. You have to take these values into account to get proper measurements along the way. There may be objects in the way of your measurements.
Cattails are a major problem that is difficult to get around.
One way to take that measurement is to physically go into the cattails in waders and plot points that way. If the student is uncomfortable in doing that then, take measurements as best as can be.