The horizontal size at the top of the lake is proportional to the square root of the surface area, as it’s a one-dimensional representation of a two-dimensional quantity.
Mean depth is represented by vertical size 1/4 and 3/4 of the way across the lake.
Note that color on this graph does not translate directly to the color of water; at this color, already enough light has been absorbed by water above such that photosynthesis can no longer be sustained, and at this color, the lake is actually pitch black.
Note also that areas on this graph are not in proportion with volumes of water the corresponding actual lakes hold, as vertical distance is much more pronounced than horizontal distance on this graph. Crater Lake is still about 14 times longer across than deep.
This image made using Raphael.js.