Differences Between a Lake and a Lagoon

Lakes are bodies of water, which are almost always a majority of freshwater. They can be very large, but they are always separated from the sea. The water in lakes can come from both rivers and streams, as well as from groundwater or rain.

Not only do they have a water inlet, but they also have outlets in the form of rivers or other channels which connect to the sea. This means the water is never stagnant, but rather there is a current, even if it is often not perceptible. There are salt lakes that are high in salinity, but the salt doesn't come from sea water. If it is a lake, it is not part of a sea.

At this point, it should be noted that those very large lakes that do not have access to the sea can also be known as a closed sea. Perhaps the most classic example is that of the Caspian Sea, which is actually a lake. Lakes play crucial roles in their ecosystems, supporting a wide variety of aquatic life and providing water resources for human use.

Lagoons are natural water deposits separated from the sea, but always in coastal regions. They are shallow, and their waters are either salty or brackish. As a result of their shallow depth and sedimentation, lagoons are usually places where a lot of vegetation grows and are home to a large amount of fauna. Unlike lakes, where only plants grow on the margins, the lagoon can contain rooted plants along its entire length.

Now that we know the definitions of a lake and a lagoon, it is likely that we still have questions about their differences. Below we explain them in detail so you can have an easy comparison between a lake vs. lagoon. Lagoons often serve as critical habitats for a wide range of wildlife, including migratory birds, and they can be sensitive to environmental changes due to their unique ecological characteristics.

In general terms, the differences between a lake and a lagoon are the following:

• Differences in depth
• Whether the water is stagnant
• Whether they are fresh or salt water
• Water temperature
• Dewatering

Next, we will explain in detail the differences between lake and lagoon for each of these aspects.

Depth

Although many people believe a key element is size, the reality is that the most important factor to establish whether it is a lake or a lagoon is depth. The shallowness of the lagoons is an essential difference from a lake. It is not possible to establish clear limits, as these depend on the area and the country. For example, in Spain, the limit is marked at 15 m, while in the US, the limit depth is 3 m. Despite these differences, a lagoon is always shallow, unlike a lake, which is always deeper. However, it is true that, in general, a lake is bigger than a lagoon.

Furthermore, the deeper nature of lakes allows for the formation of distinct ecological zones within the water column, supporting diverse aquatic organisms that require different environmental conditions.

Stagnant water

The lagoon only has a water inlet and no outlet, while the lake has both inlets and outlets. In lakes, most of the time, more water enters than leaves. If this didn't happen, they would disappear. Although there may be a sensation of stagnant water, in reality, it is in constant movement. Unlike lakes, lagoons are stagnant bodies of water, which can lead to different ecological dynamics.

Fresh or salt water

Although this is a key difference, salinity is not a 100% reliable distinction between lakes and lagoons. This is because we find water of a different nature in both lakes and lagoons. It can serve as a guiding factor when establishing the differences between a lake and a lagoon.

In general, lagoons are salt water, either because they are located next to the sea, separated by an arm of land, or because their sedimentation provides some salts that this nature gives them. For their part, lakes are usually freshwater. Salt lakes can have various deposits of salt from other sources. The salinity of lagoons often influences the types of species that can thrive there, making them unique ecosystems.

Water temperature

This is related to the point of depth. As the lagoons are very shallow, the sun's rays heat their waters evenly, so all the water has the same temperature. The difference between the lagoon and the lake is that the latter, as it is deeper, creates different temperature layers depending on the depth of the water. In general, the surface waters are warmer, while the lower ones are colder.

The stratification of lakes based on temperature can significantly affect the distribution of nutrients and oxygen, influencing the types of organisms that can inhabit different layers.

Dewatering

As we have already explained, one of the differences between a lake and a lagoon is that lagoons do not have a water outlet. Whether due to a drought or another reason, when the lagoon fails to feed itself with water, it will end up disappearing. This leads us to ask what are the differences between the dewatering of the lagoon and the lake? While the lagoons evaporate or filter out water, lakes disappear when more water leaves towards the rivers and streams than enters through other sources.

Additionally, the presence of an outlet in lakes often ensures a more stable water level, which can be crucial for sustaining human activities and wildlife habitats.

Learn more information about different bodies of water with our guide to inland waters.

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