The correct answer is option 1: Hooghly. An estuary is a partially enclosed coastal body of water where freshwater from rivers meets and mixes with saltwater from the ocean. The Hooghly River is a distributary of the Ganges River in India. It flows through the Indian states of West Bengal and has a large estuary at its mouth, near the Bay of Bengal. The Hooghly estuary is considered the largest estuary in India, making option 1 the correct answer.

Option 2, Bhagirathi, is incorrect as Bhagirathi is a tributary of the Ganges River and does not have a significant estuary of its own. Option 3, Godavari, is incorrect as it is located on the eastern coast of India and does not have a large estuary. Option 4, Krishna, is incorrect as the Krishna River also does not have a large estuary.