The Indian River Lagoon

A lagoon is a shallow water body that is separated from the ocean by a barrier and has limited connection to the open ocean. It is a special type of estuary (partially enclosed area of water that opens into the ocean and has freshwater inflows).

The Indian River Lagoon extends from the Ponce de Leon Inlet in the north to the Jupiter Inlet in the south along Florida's east coast. The lagoon system includes several interconnected water bodies such as Mosquito Lagoon, the Banana River, and Hobe Sound, and their associated estuarine areas, marshes, and mangrove forests.

The Indian River is located in a biogeographic transition between the temperate and the subtropical zones and is the most biodiverse estuary in North America. To date, over 2,200 plant and 2,100 animal species, including 700 fish species, and 310 bird species have been recorded from the lagoon.

Except for the man-made Intracoastal Waterway, the Indian River is very shallow, with an average depth of less than 1m. In this area of Florida, the continental shelf is very narrow, so ocean tides do not change very much as they approach land. This results in ocean tidal ranges (roughly, the difference in water levels between high and low tides) of only about three feet. Because of the restricted connections with the ocean, tidal ranges in the lagoon are often much narrower. In locations far from inlets, wind-driven tides are often more important than lunar tides.

Effects of Wind upon Lagoon Water Levels

Wind Speed (kts) Set-Up (ft) Set-Down (ft)
20 +1.0 -1.0
25 +1.7 -2.1
30 +2.1 -2.8
Set-up is the rise on the downwind side setdown the drop in the upwind side.
Source: Woodward & Clyde Engr.

Environmental Impacts

Major impacts to the lagoon include:

  • Habitat loss due to shoreline development and navigation improvements.
  • Pollution from point (e.g. sewage treatment plants) and non-point (e.g. undirected runoff) sources.
  • Alteration in the natural patterns of circulation and water fresh flow into the lagoon.

The shallow nature, restricted ocean connections, and narrow tides make the lagoon very susceptible to nutrient over-enrichment and suspended particle overloading. These conditions may irreversibly change the character of the lagoon, and may eliminate the aquatic macrophytes (seagrasses and macroalgae) that form the base of the lagoon food webs.