n the eastern edge of Kolkata, near the smoking mountain of the city’s garbage dump, the 15 million-strong metropolis dissolves into a watery landscape of channels and lagoons, ribboned by highways. This patchwork of ponds might seem like an unlikely place to find inspiration for the future of sustainable cities, but that’s exactly what Julia Watson sees in the marshy muddle. The network of pools, she explains, are bheris, shallow, flat-bottomed fish ponds that are fed by 700m litres of raw sewage every day – half the city’s output. The ponds produce 13,000 tonnes of fish each year. But the system, which has been operating for a century, doesn’t just produce a huge amount of fish – it treats the city’s wastewater, fertilises nearby rice fields, and employs 80,000 fishermen within a cooperative. Watson, a landscape architect, says it saves around $22m (£18m) a year on the cost of a conventional wastewater treatment plant, while cutting down on transport, as the fish are sold in local markets. “It is the perfect symbiotic solution,” she says. “It operates entirely without chemicals, seeing fish, algae and bacteria working together to form a sustainable, ecologically balanced engine for the city.” The wastewater bheris of the east Kolkata wetlands are one of the many examples of light-footed ecological practice that Watson has brought together in a new book, Lo-TEK: Design by Radical Indigenism. The TEK stands not for technology, but “traditional ecological knowledge”, something Watson thinks the so-called developed world could do well to learn from. “We are obsessed with technocratic solutions to mitigating the effects of climate change,” she says. “But a lot of the answers are already there, and have been for generations. We just have to look.” Many of the phenomena were never intended to be solutions to ecological breakdown, but simple responses to local circumstance, practised for generations. Some are bound up in millennia-old mythologies and religious practice, while others, such as Kolkata’s thriving aquaculture system, were the result of happy accident. According to local legend, in the 1920s a cultivator named Bidu Sarkar realised untreated wastewater from sewage pipes had started to flow into his fish pond. He expected disaster, but instead of killing his fish, the effluent doubled his yields. Others took note and followed his lead, realising the combination of sewage in the water and sunshine broke down the effluent and allowed plankton, which fish feed on, to grow exponentially. The fishponds now cover around 3,000 hectares, holding 300 fish farms, and the technique has caught on elsewhere in the world – in Bangladesh, Pakistan, Myanmar, Thailand, Germany and France. “As landscape architects,” says Watson, “we are asked to design artificial wetlands in cities all the time. The Kolkata bheris show how they could serve a wider purpose and be productive spaces, too.” Her book is the result of a decade of travelling to some of the most remote regions on the planet, interviewing anthropologists, scientists and tribe members. She carefully documented their indigenous innovations using the landscape architect’s language of plans, cross-sections and exploded isometric diagrams to explain clearly how they work. The 18 case studies are split into four sections, covering mountains, forests, deserts and wetlands. They range from the living root bridges of the Khasi people in India, to ancient Persian qanat underground aqueducts, to the floating thatched villages of the Ma’dan in Iraq. The compendium has come at a critical time: Watson says many of the practices are now under threat from a combination of urban development, tourism and misplaced conservation strategies. “I think we’ve got our priorities wrong,” she says. “We value and preserve the architectural artefacts of dead cultures, like the pyramids of Giza, but those of the living are being displaced and forgotten.” She is critical of the unintended impacts of the conservation movement, driven by a desire to “save nature” but which, in the process, has turned landscapes into guarded wildernesses, from which human life has been eradicated. As she writes in the book, the movement has “removed stewards, erased knowledge and ignored resilient technologies that had been mitigating climate challenges for thousands of years”. And this has spawned a new population of displaced conservation refugees. Many places in her global catalogue look like wonders of the world, on a par with the pyramids. Take the jingkieng dieng jri, the rubber-tree bridges grown over generations by the Khasi tribe of Meghalaya in north-eastern India. In a practice dating back to 100BC, the sinuous roots of rubber fig trees are trained over a scaffolding made from betel nut tree trunks, their centres hollowed out to provide a protective casing for the roots. Dangling aerial roots are woven into truss-like supports, then flat stones are laid across to form a solid deck. Over the course of their growth, the roots respond to the natural forces of the turbulent monsoon rivers, growing thicker and rooting deeper, making them extraordinarily efficient at load bearing. It is a form of slow infrastructure, with bridges planned a decade in advance, as rubber fig trees are planted at critical crossing points along rivers. This strategic planting is then used by future generations. The tradition has survived, in part, because it is inextricably linked with the origin story of the Khasi, who believe their ancestors descended from a living root ladder that connected heaven and Earth, made of a rubber fig tree. The tree is considered sacred and, with it, the practice of bridge-building and ladder-weaving has been perpetuated in a fusion of mythology and technology that preserves culture, ecology and a way of life. Watson describes how a similar spiritual reverence for the natural landscape has helped to conserve the subak rice terraces in Bali. In the steeply sloping volcanic hills, planting cycles are coordinated by a network of water temples, whose priests determine irrigation schedules according to calendrical rites. Before a fallow period, upstream temples release water into channels that feed a network of tiered terraces below. When all the fields are emptied simultaneously, pests migrating in search of food are eradicated. The effectiveness of this traditional system became all too apparent when the Indonesian government implemented a Green Revolution in the 1970s, bringing the use of massive quantities of fertiliser and pesticide to the rice terraces and ignoring the role of the water temples. Within a few seasons, yields plummeted, soil structure degraded, biodiversity diminished and the pests returned. The policy was abandoned in 1988, allowing the farmer-priests to return to their customary methods, and the area received Unesco World Heritage status in 2012. (This has come with its own set of problems, triggering an influx of tourists and stimulating development nearby.) The indigenous wisdom goes on. As bitcoin-funded “seasteaders” race to build their hi-tech floating islands on concrete and steel rafts around the world, they would do well to look to Lake Titicaca in Peru, where floating structures are made from the dense matted roots of totora reeds. Each island is simultaneously a floating village, an aquaculture farm and an artificial wetland synthesised into a single living infrastructure. Similarly, the new generation of “smart cities” planned for the deserts of the Middle East could learn from the waffle gardens of the Zuni people in New Mexico, whose sunken plots capture rainwater and runoff in the desert. They hold the water in the ground longer and slow down evaporation. Elsewhere, rather than building billion-dollar sea walls, coastal cities facing rising sea levels could look to the soft infrastructure already used for centuries by delta communities in their own countries. “We are exporting hugely expensive systems from rich, first-world nations to mitigate these natural disasters in the global south,” says Watson, “when often there are indigenous solutions that would be much more appropriate and easier to maintain. In the huge global effort to move towards climate resilience, we have to look at existing local technologies and amplify their potential. We need to transform our relationship with nature from superior to symbiotic.”