The term lagoon does not have a clear definition, and its hardly used consistently. So many factors are involved in defining lagoons that it is difficult to find a general definition that has few exceptions. A tropical lagoon is bordered by land on at least one side and is blocked from the sea by different types of barriers. These barriers, in addition to protecting the lagoon, somewhat restrict water circulation. Lagoons are typically a shallow body of marine water that may be brackish, normal, or hypersaline and do not have a major point source of fresh water input, such as a river, but do collect fresh water as it comes from the land through storm water runoff or small streams. The sediment that collects is finer-grained than near by higher-energy depositional environments. Tropical lagoons are those in which the above definition applies and reside between 30 degrees north Latitude and 30 degrees south latitude.
There are five major types of modern tropical lagoons. The five types are coastal lagoons, back-reef lagoons, inter-reef lagoons, shelf lagoons, and atoll lagoons. The differences between these lagoons are the nature of the barriers that provide protection for the lagoon and the way that these barriers are related to the mainland. Table 1 lists the general characteristics of the five lagoon types. Coastal lagoons are lagoons in which the barriers are either connected to, or are very close to the landmass. A good example of a coastal lagoon is that of Lagartos Lagoon in the Gulf of Mexico by Yucatan, Mexico. (fig. 2) The barrier on a back-reef lagoon is near to the landmass and is close to parallel with the landmass like those found in Honduras. (fig. 3) Inter-reef lagoons have barriers, reef complexes, which form on broad platforms and may not have land nearby. These lagoons are those seen between reef complexes and are found in places like Campeche Bank in Mexico.