The creeks are sometimes difficult to navigate (Photos: Sanjoy Ghosh)
The 2008 attacks in Mumbai (Bombay) were carried out by gunmen who travelled by boat from Karachi on Pakistan's southern coast. The BBC's Soutik Biswas went to the water border in the state of Gujarat to find out how India is securing its sea frontier.
Deep inside a creek close to India's western border with Pakistan, speedboat-borne commandos are firing at targets propped up in a mangrove.
It seems an unusual place for target practice - the middle of a vast, choppy creek, surrounded by water and dotted with mangroves and marshes.
We are close to Sir Creek which lies between India's western Gujarat state and the southern Pakistani province of Sindh. It has been a point of contention in the long-running dispute between the testy neighbours.
India says the creek boundary should be in the middle of the 68km (42-mile) estuary. Pakistan says the border should lie on the south-east bank.
But, arguments aside, considering that the 2008 Mumbai attacks were mounted by men who arrived by boat from Karachi, Indian security forces are taking no chances with the country's main water borders.
A handpicked team of 50 soldiers from the paramilitary Border Security Forces (BSF) have now been trained as a crack commando outfit called the Creek Crocodile Commandos to secure the area.
They provide the much-needed muscle to the troops' efforts to bolster surveillance of the sensitive water borders in the creeks.
With more than a dozen border outposts, including a few "floating border outposts" housed in small ships patrolling the creek, and now the commandos, the water borders are guarded round the clock.
"It is difficult terrain to patrol, but we take no chances with our multi-layered, heightened security," says BSF Commandant Pushpendrasinh Rathore.
I travelled into the network of creeks with Commandant Rathore and his commandos to have a look at the terrain and the challenges troops face in securing the waters.
In Gujarat's Kutch area, some 10 creeks open up into the Arabian Sea. They occupy an area of more than 4,000 sq km (2,500 sq miles) and are up to 17m (50-feet) deep.
Navigating the creeks even on speedboats and marine rafts can be difficult.
The waters turn very choppy during high tide - our speedboat rode the waves in what was sometimes a gut-wrenching and turbulent ride. At one point the boat nearly ran aground as water levels thinned out in the middle of the creek.
That is not all. Shifting sandbars change the course of channels. Sinking sand makes it difficult to patrol the marshes. It is easy for the "enemy" to infiltrate such a vast area dotted with mangroves, channels and mud flats.
So it is a minor miracle that there is a permanent security outpost in the middle of a creek, nestling in a high outcrop of land in a marsh.
The Sawla Peer outpost where more than a dozen soldiers live is not for the faint-hearted - during high tide, water inundates the marsh and the place is infested by the highly venomous Russell's viper.
Soldiers posted on the marsh said they had killed a nest of 35 vipers the day before we arrived. Snakes pose a clear danger - anti-venom is kept at hand, and mongrel dogs have been shipped in from the mainland and set free to spot snakes.
"The dogs always bark when they spot the snakes. So we can go out and kill them. They have now begun eating the snakes too," says a soldier.
Around midday, we reach Sir Creek, a 68km-long channel.
India regards the middle of the channel as the "international border". A speck on the horizon is an outpost of the Pakistan Marines, who patrol their waters. A Pakistani fishing boat is sailing at a distance.
Soldiers are posted in the marsh to guard the water border
For all the dispute around the channel, there has been no incident in the creek involving the two countries.
The only time it was in the news was in 1991 when a Pakistani surveillance aircraft flying over the creek was shot down by the Indian air force. India said the plane had strayed into its airspace.
On the way back to the mainland in Koteswar straddling the Kori creek, we spot an Indian fishing boat which has strayed into the waters and is gently admonished and turned back.
Since last October, at least 12 Pakistani nationals - who say they are fishermen - have been arrested in the creeks, boats and other equipment have also been seized. Of these, seven Pakistanis were held some 30 nautical miles inside Sir Creek. They were all handed over to the police.
Commandant Rathore is not complacent: "We have to keep a constant vigil. Who would have thought that Mumbai would be attacked by men coming in by boat?"