The islets are of volcanic origin, they were formed when the Mombacho volcano blew much of its cone into the lake thousands of years ago, thereby creating the archipelago. Most of the islets are covered with vegetation and rich with bird life.
Many of the islets are occupied. Some are privately owned and hold homes or vacation houses. There are facilities for the residents and for tourists. Hotels and shops are established on some of the islets, and boating tours are available.