This is a natural Solution Hole in Everglades Park. These are sunken areas where the limestone has dissolved underneath the coral rock causing it to collapse.
They may have standing water in the bottom, which is often at groundwater level. You will find many tree species, Chapman’s Cassia, Quailberry, Ferns, Locustberry and wildflowers taking advantage of the moisture. These are watering holes for local birds and wildlife.
The appearance of a Solution Hole can be easily created with various sizes of limerock, or even cement lining a small pit. Don’t forget to add mosquito fish if the water pools for more than two days.