Lagoons and Estuaries: What Differentiates These Bodies of Water

The Indian River Lagoon is well-known as the most biodiverse estuary in North America. This fact makes the Indian River Lagoon a great place to enjoy a day out boating. But you may be wondering, what exactly is the difference between a lagoon and an estuary?


Usually running along a shoreline and longer than they are wide, lagoons are shallow bodies of water that provide access to the sea. While they don’t generally have large rivers that flow into them, some of the very large lagoons can have that feature. The fact that they are so shallow means that they are more susceptible to changes in precipitation, evaporation, and wind, creating varied changes in salinity, the saltiness or salt that has dissolved in the body of water, and the temperature of the water. The salt content of the water can also be altered by tidal exchange and the inflow of fresh water.

Lagoons are classified into two categories; coastal lagoons and oceanic or atoll lagoons. Coastal lagoons are shallow bodies of water that, as their name suggests, exist on the coast. They are separated from the ocean by coral reefs, barrier islands, sand bar or sand splits, shingles, or rocks. Coastal lagoons can be either partly or entirely enclosed by the barrier, whatever it may be, and many show variations of salinity throughout the year. Oceanic or atoll lagoons are surrounded by a circular coral reef or a string of coral islands. These are the deeper of the two categories of lagoons.

Lagoons are also classified into three separate types; choked lagoons, restricted lagoons, and leaky lagoons. Choked lagoons feature a narrower channel and are located where there is a high energy of waves in the sea. The narrow inlet it features blocks the tides from the transferring of water from the sea to the lagoon and mixing of the water.

Restricted lagoons feature multiple channels out to the sea. These lagoons see surface currents due to wind which causes the water from the sea and the lagoon to mix, differentiating it from choked lagoons.

Leaky lagoons feature a wider channel to the sea and have fast water currents. This is the type of lagoon where you will see the most mixing of water.


The point where a river and the sea meet is called an estuary. The seawater is brought into the estuary by the tides and then is mixed in with the freshwater of a stream or river which dilutes the seawater. An estuary can be partly enclosed by a barrier but is not completely closed off from the sea. Essentially, an estuary is a body of water that serves as a transition area between land to sea and freshwater to seawater.

There are typically three zones of an estuary. The difference between the zones depends on the amount of freshwater or saltwater there is. The closer the zone is to the river or stream, the most freshwater it will have. The closer the zone is to the ocean, the more saltwater it will feature. The first zone is at the point where the freshwater of the river and the saltwater of the sea meet. In this zone, there is more freshwater than saltwater. The second zone is closer to the sea. This zone features a much more equal mix of freshwater and saltwater. The third and final zone is at the point that the water flows from the estuary into the sea. As it is closer to the ocean, this zone is mostly made up of saltwater.

Key Differences Between Lagoons and Estuaries

Lagoons and estuaries are often confused for each other as they feature similar aspects. But there are some key differences. One of those aspects is the rate of flow of the water within the bodies. While estuaries are deeper and have fast and strong currents, lagoons are shallow and the flow of water is much slower.

Despite its name and the fact that it does have shallow water, the Indian River Lagoon is actually an estuary. This is what allows it to be the most biodiverse estuary in North America. It is separated from the Atlantic Ocean by barrier islands. If you are looking to explore the Indian River Lagoon, come to 321 Boat Club for a wide selection of quality boats.