American alligators excavate depressions in marl and peat with snout, feet and tail, and maintain them by repeatedly clearing vegetation and sediment. The resulting gator holes are typically a few metres across and hold standing water long after the surrounding marsh surface has dried.
In the Everglades and comparable systems these become dry-season refuges. Fish, amphibians, aquatic invertebrates and turtles persist in them, and wading birds forage at the margins. Nutrient concentrations and plant communities in and around the holes differ measurably from the surrounding marsh, so the effect extends beyond animals. This influence on habitat availability is the basis for calling the alligator a keystone species.
The species itself was protected under United States endangered species law in 1967 after heavy hunting for hides, and removed from the endangered list in 1987. It is still listed as threatened by similarity of appearance, a legal category that protects lookalike crocodilians from trade rather than a statement about alligator numbers.