Differences Between Sea And Lake

Although it has sea in its name, the Caspian Sea is a lake as it is not connected to the ocean.
Although it has sea in its name, the Caspian Sea is a lake as it is not connected to the ocean.

Almost anybody has an idea of what a sea or a lake is. However, the confusion sets in when some water bodies referred to as seas are also called lakes. A popular example, the Caspian Sea, is considered the world’s largest lake. The Dead Sea is also referred to as a sea yet it is one of the world’s saltiest lakes. The Aral Sea, located between Uzbekistan and Kazakhstan, is also a lake. Although the concept of “lake” and “sea” can be confusing, there are fundamental differences between the two bodies of water.

The major differences between a lake and a sea are;

  • A lake is enclosed on all sides by land and does not connect to a larger water body like an ocean, while a sea connects to an ocean.
  • A sea is much larger and deeper than a lake
  • A lake is either natural or artificial, while a sea occurs naturally
  • A sea contains only salty water, while a lake can contain either salty or freshwater

The differences have been explained in greater detail below:

Brief Definition Of Sea And Lake

Mediterranean Sea map
Although the Mediterranean and Black Sea appear to be enclosed by land on all sides, they are connected to the Atlantic Ocean via straits. Hence, they are both true seas. 

A lake is a stagnant, deep, hollow body of water enclosed on all sides by land. It is an inland water body with many sources or inlets of different characteristics, including rivers and streams. Lakes do not open or connect to any other planet reservoir or large water bodies such as oceans and sea. They are either naturally formed or artificial and are of different types, including tectonic and highland lakes.

On the contrary, a sea is a water body directly connected to a larger body of water - the ocean. Thus, a sea is a continuous stretch of water, mainly salty water opening to or emptying its waters in an ocean. Seas are broadly classified as internal or external. Internal seas, like the Mediterranean and the Black Sea, are almost enclosed by mainland and have access to the ocean via a strait. External seas, such as the Caribbean, are in the form of bays surrounded by islands.

Capian and Aral Sea maps
Although the Caspian Sea and Aral Sea have sea in their names, they are lakes as they are not connected to the ocean.

Size And Depth

Lakes are usually small, medium, or large in size, with water exposed towards the surface. The topography, size, and shapes of most lakes change over time, by either shrinking or overgrowing. Some lakes can even turn into swamps or dry up and disappear if inflow is cut off or insufficient. Most world lakes are shallower and have a surface area of below 100 square miles. However, a few lakes cover over 1.500 square miles.

On the other hand, seas are much bigger and deeper than lakes. They carry larger volumes of water than most lakes. Because of their sizes and connection to World Ocean, it is not easy for seas to dry up or disappear. 

Type Of Water

Seas contain salty or saline waters, meaning they are always salty. One kilogram of seawater contains approximately 35 grams of various sea salts, including sodium chloride, magnesium sulfate, and magnesium chloride. The sea saltiness result from salt and minerals deposited by rivers flowing into the ocean or sea.

Dead Sea
The Dead Sea is the most saline lake in the world.

Lakes contain either fresh or saline water. Thus, there are freshwater lakes and saline lakes. The Dead Sea is the world’s most saline lake. Freshwater lakes contain freshwater because they are frequently replenished by rain or water flow in and out of them constantly. On the other hand, some lakes are salty because they do not have an outlet. Therefore, since rivers carry salt and other minerals into the lakes, as water evaporates, salts are left behind.


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