This section is from the book "British Wild Flowers - In Their Natural Haunts Vol2-4", by A. R. Horwood. Also available from Amazon: A British Wild Flowers In Their Natural Haunts.
The particular form of aquatic vegetation will at once determine the mode of survey. In a pond or lake the vegetation is generally concentric, hence the mapping must be done on such lines; whilst in a river, stream, or ditch it forms more or less parallel bands or zones, and should be done by making cross-sections (as indeed may be done in the first case).
The division of aquatic vegetation into zones of floating, submerged, and reed-swamp associations renders it necessary to study them by these zones. Any one may be studied by itself, or all the zones together. In either case the dominance of any particular plant should be noted.
Such points as the character of the mineral salts in the water should be studied by advanced students.
The rate or character of the current should be noticed. The juxtaposition of the different societies should be noted at different points. In the case of wet places they may be studied in the same way as meadows and pastures, and the tape or stakes may be used for marking out squares to be studied one by one in detail.
The zones that lie deepest in the water can only be studied by aid of a boat, and this maybe a difficulty not easily overcome. The dredge may be used to examine not only the lowest zones of flowering plants but also the plankton, which occurs at the surface.