Water slaps against the sides of the seventy-foot metal boat, the Golpata, as I descend the ladder on its side and step onto a smaller, almond-shaped wooden vessel in total darkness. It is August 2014, and the monsoon season is upon the delta.

There is no moon; the river reflects a cloche of a billion twinkling stars. The chizzzzzz of crickets is an almost meditative backdrop punctuated by the tokey-tokey-tokey call of the tokay gecko and the gentle splosh of oars slicing into water as Mujibur rows away from the Golpata and the boat arcs, in a graceful ellipse, into a tiny khal.

Mujibur is my guide, spotter, coffee-maker and oarsman. The khal we enter is among the last of the offshoot channels before the many tongues of the Sela river open into the Bay of Bengal, in Bangladesh. The channel we row through is narrow, and hemmed in by towers of pneumatophores – aerial roots that act like snorkels for mangrove trees – ghostly-white in the glow of my flashlight. Some shoot straight up like spear points, others curve in the air, some are stumpy and thick while still others have curlicued designs on them. Each belongs to a different species of mangrove tree, but their purpose is the same – they help the trees breathe during the twice-daily dunking in brackish water as the high tide pushes the sea in.

Calcified star-shaped cones of barnacles cling to nipa palm trees (after which our boat, the Golpata, is named) just above the high tide mark. Huge mud crabs and tiny pink fiddler crabs scuttle and bury themselves in the ashen mudflats that shine in my flashlight’s reflected glow. As we go deeper into the khal, the dense vegetation leeches away even the little light there is; we are in a blackhole where sight is useless and the only sense left is aural. Some sort of creature walks on leaf litter in the forest to my left, its steps going chush-chush-chush. Two bright green circles of tapetum flash briefly and vanish just as quickly. The boat creaks ahead, the reflected stars dance in its wake and the tide continues to rise.

We are deep in the Sundarban, the largest unbroken mangrove forest in the world. They call it the “land of eighteen tides”. It is the part-forested, part-settled delta of three mighty rivers – the Ganga, Brahmaputra and Meghna – and straddles the border between India and Bangladesh. Mangroves are both land reclaimers and builders. The rivers of the Indian subcontinent that originate in the Himalayan range are soupy with the silt they accrete and cart across thousands of kilometres, making the Ganga and Brahmaputra among the siltiest rivers in the world.

They offload some of the silt along their course, creating fertile floodplains and food bowls before they end up here in the Sundarban. This is where the silt settles, layer upon layer, enriching the soil and creating a conducive environment for the mangroves.

The mangrove’s roots – some hanging low like talons, some spreading far like tentacles, others upturned like gnarled fingers poking out of the water – grab the silt and fashion islands that over time link up, eventually merging with the mainland. These islands of silt are technically neither land nor water; they are suspended in the middle realm, ready to be reclaimed at will by the river and rushed into the sea. These ephemeral marginlands balance precariously between the sweet of the river and the brine of the sea, and form the coastal defence against the cyclone-prone “beating heart of monsoon Asia”, the Bay of Bengal.

The Bay is known for the viciousness of the storms it unleashes each monsoon – Sidr (2007), Aila (2009), and Amphan (2020) are merely the best-known examples. These cyclones bring with them sea surges – giant walls of water fifteen feet high – that race inland and sweep aside people and houses, boats and farms and everything else it finds in its path. It is the mangrove swamps of the Sundarban that can abate such surges and lessen their impact on the hamlets inland. The snaking roots of the mangrove cling to the mudflats, anchoring them in place and keeping the soil from being washed away.

The turgid sea batters these mudflats and dissipates much of its venom into the impassable barrier of the dense mangroves, which bear the lash of wind and the surge of tide that would otherwise strike at the cities of Khulna in Bangladesh and Kolkata in India which sit along the Sundarban’s northern boundaries. This soupy, silty, eternally shifting landscape is a burgeoning nursery of life where, among the mangrove roots, fish grow, prawns spawn and crustaceans thrive. These mudflat forests have sustained humans for centuries, providing fertile waters for fishing, forests of timber, and flowers for wild honey.

Ruling over this idyllic environment is the storied hilsa, an Indian shad that swims upriver to spawn and lives out its adult life in estuaries like the Sundarban. It is a monsoon fish and a cultural icon of Bengal. No wedding feast is complete without it. The hilsa is the centrepiece of Durga Pujo, the autumn festival that celebrates the goddess Durga in the region. As a travel writer once said, “If Bengali cuisine were Wimbledon, the Hilsa would always play on Centre Court.”

Everywhere I have gone, I have met Bengalis who would tell me of bygone times when they could plunge their hand into the Meghna or the Podda rivers (the Ganga takes the name Padma in Bangladesh, which in Bengali is pronounced pod-da) and come up with a shimmering 2.5-kilogram ilish maachh. An elderly lady in Kolkata once told me that they don’t take the fish’s name when they step out to buy ilish. “I’m going to get him,” they instead say, and the message is never not clear. But increasingly such narratives are tinged with a forlorn nostalgia as this king among fish disappears from its habitat.

Back on the Golpata which is moored in the middle of this khal on the cusp of the Bay of Bengal, we sit down to a dinner of curried prawns and vegetables, fried eggplant, pappadams, and lentils. A sudden gust turns the boat into a rocking chair. The Golpata is clearly not meant to be a sea-going vessel. “Our boat will not last two days in these waves,” Alom, the boatmaster, says. About a furlong ahead, we spot a large, traditional wooden fishing trawler (not one of the mechanised ones that are the bane of all artisanal fishermen) bobbing in the waves. Butterscotch-coloured buoys are piled up on its deck and, in the weak light of swaying yellow lanterns that throw more shadows than light, we see several men silhouetted against diaphanous white fishing nets.

After dinner, we pull up alongside. The silhouettes grow faces which fill out in smiles of welcome. More men come out from the cabin amidships; we are now close enough to read the name of the boat – Mayer Doa (“mother’s blessings”). The trawler’s cook opens a door aft of the boat, carved with a kolohi or kalash, and fires up his stove to make laal saa – the red, milk-less tea that is a mandatory accessory for conversation. A man in his mid-thirties comes forward and introduces himself. Sultan is the boat’s owner, a hilsa fisherman operating the Mayer Doa with his crew of 14. The most lucrative fishing window is in the monsoon months when the freshet in the rivers is strong and the hilsa swim against it, going upriver to spawn. In days gone by, the season was so lucrative that fishermen specialised in the hilsa; in season, they made so much money that they did not have to work for the rest of the year.

Sultan’s boat is in its first season. He had bought it for 13 lakh taka (about $15,000); the specialised hilsa nets cost a further ten lakh taka (roughly $12,000). Sultan is deep in debt, but it wouldn’t have mattered if the season was conducive. It has been anything but – the Mayer Doa has been on the high seas for two days now, and they have just ten kilograms of hilsa to show for their labours, not even one fish per crew member. Sultan’s debt now looms ominously, a crushing burden he knows he cannot overcome.

“When we were young,” says Noor Miyan, an older crew member, “we’d go out for an hour and come back with enough fish for a day. But now we go for eight hours, we fish deeper, farther out, and still come back with less than half the fish compared to my younger days.”

Excerpted with permission from Marginlands: Indian Landscapes on the Brink, Arati Kumar-Rao, Picador India.