A stretch of sea water partly or fully separated from the main sea by a narrow strip of land is called what?

Introduction / Context:
Coastal landforms are shaped by the interaction of waves, tides, currents and sedimentation. Many specific terms describe different features along the coastline, and these are frequently tested in physical geography sections of exams. One important feature is a body of sea water that is partly or completely separated from the open sea by a narrow strip of land such as a sandbar, reef or barrier island. This question asks you to identify the correct term for such a feature, and knowing the distinction between terms like bay, lagoon, isthmus and strait is essential.

Given Data / Assumptions:

• The water body is a stretch of sea water.
• It is partly or wholly separated from the main sea.
• The separation is by a narrow strip of land or barrier.
• The options given are bay, isthmus, lagoon and strait.

Concept / Approach:
A lagoon is a shallow stretch of sea water separated from the main sea by a barrier, which may be a sandbar, coral reef or barrier island. It often has limited exchange with the open ocean through narrow inlets. A bay, by contrast, is a wide inlet of the sea into the land and is generally more open to the main sea. An isthmus is a narrow strip of land connecting two larger land areas and separating two water bodies, not itself a water body. A strait is a narrow channel of water connecting two larger bodies of water. Since the question describes a sea water body cut off by a narrow strip, lagoon is the appropriate term.

Step-by-Step Solution:
Step 1: Focus on the description: a stretch of sea water separated from the main sea by a narrow strip of land. Step 2: Recall from coastal geography that such semi enclosed water bodies are typically called lagoons. Step 3: Understand that the narrow strip may be a sandbar, spit, reef or barrier island. Step 4: Compare this with the definitions of bay, isthmus and strait, which do not match the description exactly. Step 5: Select lagoon as the correct term for this type of sea water body.

Verification / Alternative Check:
To verify, think of specific examples like the Chilika Lake in India or the Venice Lagoon in Italy. These are shallow coastal water bodies partially separated from the open sea by sandbars or other barriers and are consistently referred to as lagoons. Bays, such as the Bay of Bengal, are much larger open inlets, while straits like the Strait of Gibraltar are narrow connecting channels between two open seas. An isthmus, like the Isthmus of Panama, is land, not water. This comparison reinforces that lagoon is the correct term for the feature described in the question.

Why Other Options Are Wrong:
A bay is a broad indentation of the sea into the coastline and is usually well open to the main sea, not separated by a narrow strip of land. An isthmus is a narrow strip of land connecting two larger landmasses and separating two bodies of water, so it is not the water body itself. A strait is a narrow passage of water connecting two larger seas or oceans, the opposite of being cut off from the main sea. Since none of these match the description of a partly enclosed stretch of sea water behind a barrier, they are incorrect options for this question.

Common Pitfalls:
Students sometimes confuse lagoons with bays or estuaries because all involve coastal water. Another error is to pick isthmus or strait simply because they involve narrow features, without focusing on whether the feature described is land or water and whether it connects or separates. To avoid such confusion, carefully read the definitions of each coastal landform and associate them with well known examples. Creating a chart comparing bays, gulfs, lagoons, estuaries, straits and isthmuses will significantly improve clarity.

Final Answer:
A stretch of sea water partly or fully separated from the main sea by a narrow strip of land is called a Lagoon, so lagoon is the correct option.