Kidney-Shaped Fiberglass Preforms have that "natural" pond shape, and make for relatively easy ground excavation and backfilling, since there are no odd-shaped edges and ends, or precise 90-degree corners. The ASL and CSL Models have a 3.5-inch deep, 6-inch wide "stone ledge," great for softening the pond edge with rock, or for planting with bog growers and marginals that enjoy shallower waters. The Y Model has a large step, making a good part of the preform only half-depth. Due to their non-geometrical shapes,specifications listed below are measured at the longest and widest points on each Kidney-Shaped Fiberglass Preform. Being generally smaller-sized, none of these pools are deep enough to weather fish for the Winter.