The lakes themselves may work as an index if you experiment with the zoom percentage. You can also experiment with how much to round the scale. Choosing to, for example, round scale to the nearest 2000 will guarantee a minimum map scale of 1:2000, but it could also mean a map page best generated at 10,500 will generate at 12000.
There are two typical problems: shapes that are too far from rectangular pages (such as super long and skinny) and shapes with outlier sizes; your tiny ones may look zoomed in too far and not include enough surrounding features, and the super large ones may not show enough detail because the scale is too small.
Methods I have used to deal with these kind of problems include excluding the outliers from the DD map index feature, copying the index feature and editing some of the shapes to get a better fit, and creating 2 DD mxd layouts, such as one for portrait and one for landscape layouts (using a layout field to select which shapes to include when). One advantage of copying a polygon feature that is your index is that you can then do a Page Query on it, which you cannot do directly on an index polygon feature.
