Tens of thousands of them feed on Thane Creek every winter, on mudflats bracketed by refineries, a container port and now a 21.8 km sea bridge. Ecologists disagree about why the numbers rose. Nobody disagrees that it is the strangest wildlife spectacle in any Indian city.
An estuary in an industrial corridor
Thane Creek is a tidal estuary separating the island city and Navi Mumbai, roughly 26 km long, fringed by one of the largest remaining mangrove belts in the Mumbai Metropolitan Region. Its shoreline is also one of the most industrialised stretches of coast in the country: refineries and petrochemical complexes at Trombay, the container terminals of Jawaharlal Nehru Port on the creek's outer approach, thermal power infrastructure, and, since its opening in January 2024, the Mumbai Trans Harbour Link, a 21.8 km sea bridge connecting Sewri to Chirle near Nhava Sheva, one of the longest sea bridges in India.
That combination — heavy industry and a major tidal wildlife habitat on the same few kilometres of shoreline — is unusual anywhere, and it is the backdrop against which the creek's most visible resident, the flamingo, has to be understood. The mudflats that draw the birds sit essentially within sight of oil storage tanks and container cranes, a juxtaposition that has become one of the more photographed contrasts in Indian urban ecology, and one that regularly surprises visitors expecting a wildlife spectacle to come with a more conventionally scenic backdrop rather than a working industrial shoreline.
In 2015, the Maharashtra government notified a substantial part of the creek as the Thane Creek Flamingo Sanctuary, extending across roughly 1,690 hectares, giving the mudflats and adjoining mangroves a formal protected status that they had lacked despite decades of seasonal flamingo presence. The notification followed years of advocacy from conservation groups and researchers who had documented the birds' growing numbers and argued that the creek's rapid industrial and urban development made a formal protective designation increasingly urgent rather than optional, particularly given how much of the surrounding shoreline had already been lost to reclamation and construction by that point.
Two species, two very different numbers
The birds seen on Thane Creek are mostly Lesser Flamingos, smaller and pinker than their better-known relative, alongside smaller numbers of Greater Flamingos, which are larger and paler. Lesser Flamingos breed at only a handful of sites worldwide, most significantly the alkaline lakes of the East African Rift Valley and the Rann of Kutch in Gujarat, and the birds seen around Mumbai in winter are generally understood to be non-breeding visitors from these populations rather than a locally breeding group, arriving to feed rather than to nest. The two species are distinguishable at a distance mainly by size and by the depth of pink in the plumage, with Lesser Flamingos generally showing the more vivid colouring of the two despite their smaller frame.
Counts vary considerably by year and by survey method, but figures commonly cited by the Bombay Natural History Society and state forest department surveys have run from the low tens of thousands up to considerably higher peaks in strong years, making Thane Creek one of the largest urban concentrations of flamingos anywhere in the world during the winter season. The birds feed by filtering algae, small crustaceans and other invertebrates from the mudflat surface using a specialised bill technique, and their pink colouration comes from carotenoid pigments in that diet rather than anything intrinsic to the bird itself.
Numbers typically build through the winter months, roughly November through to around May, tracking both the migratory calendar of the non-breeding population and the tidal and algal conditions on the creek itself, before falling away again as the birds disperse. Peak counts are generally reported somewhere in the January to March window, though the exact timing shifts from year to year depending on rainfall, tidal patterns and conditions at the birds' other feeding grounds along the west coast, which makes any single winter's count a poor guide to the following year's numbers on its own.
The disputed reason the numbers rose
Flamingo sightings on Thane Creek are not a recent phenomenon — they have been recorded for decades — but the scale of the gathering in the last twenty to thirty years, and particularly the concentration around Sewri, has grown enough to draw sustained scientific and conservation interest, and the explanation for that growth is genuinely disputed among ecologists rather than settled. What was once a modest seasonal presence noted by a handful of birdwatchers has become one of the most widely reported wildlife stories to come out of the city each winter, drawing researchers, photographers and casual visitors in numbers that would have been unimaginable a few decades ago.
One line of explanation points to nutrient loading: partially treated sewage and industrial discharge entering the creek has, on this reading, boosted the algal and microbial productivity of the mudflats, effectively feeding the flamingos' food supply even as it degrades water quality by other measures. This is an uncomfortable finding for conservationists, since it implies the very pollution pressures threatening the wider estuary may be part of what draws such large numbers of birds to feed there, complicating any straightforward call to simply reduce discharge into the creek without also considering the effect on the food supply the birds now depend on.
An alternative or additional explanation looks to habitat loss elsewhere along the west coast and in the flamingos' other traditional feeding grounds, pushing birds toward whatever large, undisturbed mudflat habitat remains, of which Thane Creek — protected since 2015 and less disturbed by fishing and human traffic than some alternatives — is one of the larger surviving examples in the region. Researchers studying the population generally treat this as an open question rather than a resolved one, and it is likely that several factors, including tidal patterns and creek-specific productivity, combine rather than any single cause dominating.
Sewri and the practical business of watching them
The most accessible and best-known viewing point is Sewri Jetty, on the eastern edge of the island city, reachable from Sewri railway station on the Harbour Line by a walk of roughly fifteen to twenty minutes. The jetty overlooks mudflats that are exposed at low tide, which is when the flamingos concentrate visibly within a workable viewing distance from the shore; at high tide the mudflats are submerged and the birds disperse further out or are simply not visible from the jetty. The jetty itself is a working structure rather than a purpose-built viewing platform, and it remains one of the few points on this stretch of coast where the public can walk right up to the water's edge.
Because visibility depends entirely on tide state rather than time of day, checking a tide table for Mumbai before travelling is more useful than any fixed visiting-hours guidance, and low tide in the early morning generally gives the best combination of light and bird activity. Binoculars or a zoom lens make a considerable difference, since even at low tide the birds feed some distance out on the flats rather than close to the jetty edge, and a naked-eye view alone tends to understate both the numbers present and the extent of the pink colouring visible on a clear day.
Entry to Sewri Jetty itself is free, and the site is an open public jetty rather than a managed sanctuary facility with its own gate or opening hours, though the formally notified Thane Creek Flamingo Sanctuary extends across a wider area of the creek than the jetty viewpoint alone covers. Boat trips out onto the creek for a closer view are periodically offered by tour operators and, at times, forest department-linked initiatives, though the jetty view alone is generally considered sufficient given the birds' concentration in the visible flats at low tide, and it avoids the added disturbance a boat can cause to feeding birds.
The bridge overhead
The Mumbai Trans Harbour Link's route crosses Thane Creek in the immediate vicinity of the flamingo feeding grounds, and its construction and planning process was contested for years on environmental grounds, including formal objections and litigation from conservation groups concerned about noise, light and physical disturbance to the mangroves and mudflats along its alignment. The final approved design included mitigation measures — sections of noise barrier and lighting design intended to reduce disturbance to the birds — negotiated during the environmental clearance process, alongside commitments around construction-phase monitoring of the surrounding mangrove and mudflat habitat.
Since the bridge opened in January 2024, monitoring of flamingo numbers and behaviour in its vicinity has continued through forest department and independent surveys, and assessments of its actual impact on the birds have varied; some observers report continued strong flamingo presence near the bridge corridor, while environmental groups continue to track the question rather than considering it closed. It remains, in that sense, an ongoing case study in whether large-scale infrastructure and a major migratory bird population can share the same few kilometres of estuary, one that planners of future coastal projects elsewhere in India are likely to watch closely.
What threatens the mudflats besides the birds' own popularity
Thane Creek sits at the centre of several overlapping pressures beyond the flamingos: continued industrial discharge from the Trombay and Taloja industrial belts, sewage from a rapidly growing Navi Mumbai population, mangrove clearance for infrastructure and, periodically, illegal landfill and encroachment along the creek's edges, which conservation groups and the Bombay High Court have addressed through litigation over the years given mangroves' additional legal protection status in Maharashtra. The court has, in several rulings over the past two decades, directed state agencies to act against illegal mangrove destruction and dumping, though enforcement across such a long and industrially active shoreline remains an acknowledged challenge.
The flamingo sanctuary notification in 2015 gave the mudflat habitat a formal legal status it previously lacked, but a sanctuary designation constrains development and disturbance rather than eliminating the upstream pollution and encroachment pressures that predate it, which is why the creek's ecological condition remains an active subject of monitoring by the state forest department, BNHS and independent researchers rather than a settled, resolved matter. Long-term water quality and mangrove-cover data, collected across multiple years by these groups, form the evidence base most current policy discussion about the creek's future actually draws on, and that record is what any claim about the creek's improving or worsening health ultimately has to be checked against.
Questions travellers ask
When is the best time to see flamingos at Sewri?
The flamingo season on Thane Creek generally runs from around November through to May, with numbers typically building over the winter months. Within that season, visibility depends on the tide rather than the calendar: low tide exposes the mudflats where the birds feed, so checking a Mumbai tide table before travelling matters more than picking a particular month or time of day.
Is Sewri Jetty free to visit?
Yes. Sewri Jetty is a public jetty rather than a ticketed sanctuary facility, and there is no entry fee to walk out and view the mudflats. It is reachable on foot from Sewri railway station on the Harbour Line in roughly fifteen to twenty minutes, and no permit or advance arrangement is needed to visit, though sightings depend entirely on the state of the tide at the time.
Why are the flamingos pink if it comes from their diet?
Flamingos filter algae, small crustaceans and other invertebrates from the mudflat surface, and many of these food sources contain carotenoid pigments, the same class of compound that colours carrots. The birds metabolise these pigments into their feathers, so their colour is a direct product of what they eat on the creek rather than a fixed trait, and captive or poorly fed flamingos elsewhere are noticeably paler.
Has the Mumbai Trans Harbour Link harmed the flamingos?
This is disputed and actively monitored rather than settled. The bridge's alignment crosses close to the birds' feeding grounds and its environmental clearance included mitigation measures for noise and light, but assessments of its real-world impact since the 2024 opening have varied, with some surveys reporting continued strong flamingo presence and conservation groups continuing to track the question through ongoing monitoring rather than treating it as resolved either way.