The largest lake in Kerala, which is also the longest lake in India, is:

Vembanad Lake is the largest lake in Kerala and is often described as the longest lake in India. It stretches about 96 km along the coast, through the Alappuzha, Kottayam and Ernakulam districts, and covers an area of about 2,000 square km including its wetlands.

Nature of the lake:

• It is a brackish-water lagoon (backwater), separated from the Arabian Sea by a narrow barrier of land, with openings to the sea at Kochi and other points.
• Several rivers, including the Pamba, Achankovil, Manimala, Meenachil, Muvattupuzha and Periyar, flow into it.

Thanneermukkom saltwater barrier:

Built in 1975 across the lake, this barrier prevents salt water from entering the southern part of the lake during the dry season, so that farmers can grow rice. However, it has also caused ecological problems.

Kuttanad:

• The Kuttanad region, around the southern part of Vembanad, is known as the "Rice Bowl of Kerala".
• Farmers here grow rice on land lying below sea level.

Tourism and culture:

Vembanad is famous for houseboat cruises from Alappuzha (Alleppey) and Kumarakom.

The Nehru Trophy Boat Race, held on the Punnamada Lake (part of Vembanad) every August, is a famous snake-boat race. It began after Jawaharlal Nehru's visit in 1952.

The Kumarakom Bird Sanctuary is on its eastern shore.

Conservation:

• Vembanad was declared a Ramsar site in 2002 (as the Vembanad-Kol Wetland), one of the largest Ramsar sites in India.
• It faces threats from reclamation, pollution, invasive weeds and shrinking area.

Kochi:

The port city of Kochi (Cochin) stands at the northern end of the lake, where it opens into the sea.

Why not the other options?

• ✗Veli Lake is a small lake near Thiruvananthapuram, and Sasthamkotta is the largest freshwater lake of Kerala.
• ✗Pookode Lake is a small freshwater lake in Wayanad.