The question asks to identify the river that serves as the sole natural water source draining into a lake within a desert region. This describes a unique characteristic of a river system that does not reach the sea but rather terminates inland, often in a lake or marshy area, especially in arid or semi-arid environments like a desert.

Understanding Rivers and Desert Drainage Systems

Most major rivers flow into larger bodies of water such as seas or oceans. However, some rivers, particularly those in dry regions, exhibit what is known as 'inland drainage'. This means their water either evaporates or sinks into the ground before reaching the sea, often ending in a lake or a dry basin within the landmass.

Analyzing the Options

Let's examine the given options:

• Teesta: The Teesta River is a major river flowing through India and Bangladesh. It is a tributary of the Brahmaputra River, which ultimately flows into the Bay of Bengal. It does not drain into a desert lake.
• Ganga: The Ganga (Ganges) is one of the largest rivers in the Indian subcontinent. It flows through India and Bangladesh and empties into the Bay of Bengal. It is a vast river system and does not drain into a lake in a desert.
• Kali: The Kali River could refer to several rivers in India and Nepal. Depending on the specific river, it either flows into larger river systems like the Ghaghara (a tributary of Ganga) or directly into the sea (like the one in Karnataka). None of the prominent Kali rivers are known to drain into a desert lake.
• Luni: The Luni River is a river of western Rajasthan state, India. It originates in the Aravalli Range and flows through the Thar Desert (Great Indian Desert). It is known for being a unique river because its water is sweet in the upper reaches but turns saline in the lower reaches due to the salt content of the desert soil. Significantly, the Luni River does not drain into the Arabian Sea. Instead, it dissipates into the marshy lands of the Rann of Kutch in Gujarat, which can be considered a form of inland drainage ending in a saline depression or lake/marsh system depending on the season. It is considered the only major river system in this part of the Thar desert with such a drainage pattern.

The Luni River: A Unique Desert River

The Luni River exemplifies inland drainage in a desert environment. It flows southwestward through the Thar Desert. Its termination in the Rann of Kutch, a salt marsh, fits the description of draining into an area that functions like a large saline lake or basin, especially during certain times of the year. This makes it the only natural water source of its kind in that specific desert region that does not outflow to the ocean.

Based on the analysis of the drainage patterns of the rivers listed, the Luni River is the one that uniquely drains into a lake-like marshy area within a desert, distinguishing it from rivers that reach the sea.

Revision Table: Key Rivers and Drainage

Additional Information on Desert Rivers

Desert environments often have unique hydrological features. Rivers flowing through deserts may be ephemeral (seasonal) or perennial. Perennial rivers in deserts often originate in wetter regions and manage to cross the desert, either reaching the sea (like the Nile crossing the Sahara) or terminating inland as the Luni River does. Inland drainage basins in deserts can form salt lakes or playas as water evaporates, leaving behind dissolved salts.