Between a barrier island and the mainland coast, fresh water from inland rivers and creeks and runoff from the land merges with salt water from the ocean to create a “brackish” lagoon, a type of “estuary.” Although definitions vary in the scientific community, estuaries have one or more free connections to the ocean, such as inlets, while lagoons have a more restricted exchange of salt and fresh water. Several factors cause variations of the level of salinity (salt) between lagoons and even within one lagoon in the same location. In periods of flooding, more fresh water comes in; in periods of drought, more salt water comes in. Although affected by moon-driven tides, estuaries are generally protected from the full force of waves, winds, and storms by surrounding reefs or barrier islands. The amount of runoff from the land and the proximity of inlets, rivers, and creeks are also influences. Because these terms are subject to ongoing examination and revision, “lagoon” and “estuary” may be used here interchangeably.

Changing ocean levels have formed some estuaries naturally, but humans have also created new ones where they have added inlets, and they have become “nurseries of the ocean” in the same way that natural estuaries are. Estuaries provide habitats for countless plants and animals and a safe escape from the predators of the open ocean.

According to maps made in the 1800s, there were once many more lakes, lagoons, and marshes in what became Palm Beach County. Lake Occossee was located north of Lake Mangonia, in West Palm Beach. Several lakes existed between today’s Lake Osborne (in Lake Worth and Lantana) and Lake Ida (in Delray Beach), including Louis Lake and Lakes Webster, Jackson, Bessie, and Boynton. From Lake Ida southward to the Hillsboro Canal, there were many ponds and lakes, which became part of the El Rio Canal (or E-4 Canal) system.

These waterways served as major highways for the county’s early residents, who built boats of varied sizes and designs to get around. Both Native Americans and more recent settlers found an abundance of fish, shellfish, and small mammals on the shore as well as in the water.