What is the Difference Between Estuary and Lagoon

The main difference between estuary and lagoon is their depth. Estuaries are deep, while lagoons, usually coastal lagoons, are comparatively shallower.

Estuaries and lagoons are two types of coastal bodies of water that share similar characteristics. Most people, even experts, tend to use these words interchangeably since there is a great overlap between them.

Key Areas Covered

1. What is an Estuary 
     – Definition, Features
2. What is a Lagoon
     – Definition, Features 
3. What is the Difference Between Estuary and Lagoon
    – Comparison of Key Differences

Key Terms

Estuary, Lagoon

What is an Estuary

An estuary is a partially enclosed coastal water body where freshwater from streams or rivers mixes with the saltwater from the ocean. The combination of seawater and freshwater results in brackish water, which is somewhat salty but not salty as seawater. Both seawater and freshwater constantly circulate in and out of estuaries. While tides generate the largest flow of saltwater, river mouths result in the largest flow of freshwater. Moreover, estuaries are typically protected from the full force of waves and winds by landforms like barrier islands and peninsulas. 

Figure 1: Amazon Estuary

There are many types of habitats in and around estuaries. These include sandy beaches, rocky shores, river deltas, shallow open water, marshes, and tidal pools. Estuaries are also home to unique plant and animal species that thrive in brackish waters.

We can categorize estuaries into four different types on the basis of their formation.

Coastal plain estuaries form when sea levels rise and fill in an existing river valley. The famous Chesapeake Bay in the United States is an example of a coastal plain estuary. California’s San Francisco Bay, on the other hand, is an example of a tectonic estuary. Such estuaries form due to tectonic activity, i.e., shifting together and rifting apart of the Earth’s crust.  Moreover, when a barrier island separates an estuary from the sea, we call it a bar-built estuary. Fjord estuaries are a form of estuaries glaciers create. They occur when glaciers carve out a deep, steep valley and then retreat while the ocean rushes in to fill the narrow, deep depression.

What is a Lagoon

A lagoon is a shallow body of water separated from the ocean by a narrow landform like barrier islands, sandbars, or coral reefs. They are common coastal features observable in many parts of the world. Bora Bora in French Polynesia, The Outer Banks on the coast of North Carolina and Virginia, and Blue Lagoon in Iceland are some popular lagoons in the world. In fact, the city of Venice is created on barrier islands and a lagoon of the Adriatic Sea.

Figure 2: Bora Bora Lagoon

Furthermore, there are two main types of lagoons as coastal lagoons and atoll lagoons. Coastal lagoons are protected by barrier islands or sandbars, while atoll lagoons are protected by coral reefs. We can further categorize coastal lagoons into three types: choked lagoons, restricted lagoons, and leaky lagoons.

Difference Between Estuary and Lagoon

Definition

An estuary is a partially enclosed coastal water body where freshwater from streams or rivers mixes with the saltwater from the ocean, while a lagoon is a shallow body of water separated from the ocean by a narrow landform like barrier islands, sandbars, or coral reefs.

Depth

Estuaries are deep, while lagoons, usually coastal lagoons, are comparatively shallower.

Currents

Moreover, estuaries tend to have fast and strong currents, while the flow of water in lagoons is much slower.

Conclusion

In brief, the main difference between estuary and lagoon is that estuaries are deep while lagoons, usually coastal lagoons, are comparatively shallower. Moreover, estuaries tend to have fast and strong currents, while the flow of water in lagoons is much slower.

Reference:

1. “Estuary.” National Geographic Society, 9 Oct. 2012.
2. “Lagoon.” Wikipedia, Wikimedia Foundation, 8 July 2021.

Image Courtesy:

1. “Mouths of amazon geocover 1990” (Public Domain) via Commons Wikimedia
2. “Boraboraluft gerade.”By Makemake (CC BY-SA 3.0) via Commons Wikimedia

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