Step 1: Understand the question.
We need where Sir Creek, a 96 km tidal estuary, is located.
Step 2: Identify it.
Sir Creek lies in the Rann of Kutch marshlands, separating Gujarat in India from Sindh in Pakistan.
Step 3: Why it matters.
It opens into the Arabian Sea and is a disputed maritime boundary between India and Pakistan.
Step 4: Rule out others.
The Hooghly-Matlah system is in West Bengal, the Godavari delta in Andhra Pradesh, and the Mandovi in Goa.
Step 5: Conclude.
Sir Creek is in the Rann of Kutch.
Answer: Rann of Kutch