Lake Chimay - the lake that never existed

The phase between the 1200s and the mid-1800s saw Mediterranean seafaring Europeans, followed by Renaissance and early-modern cartographers from France, England, Holland, the Holy Roman Empire, and the Italian kingdoms, begin mapping what they considered the 'unexplored' regions of Africa, the Americas, Asia, and Australia. In the process, they introduced several inaccuracies and errors: California was shown as an island, an imaginary southern continent was marked as Terra Australis Incognita, and the Japanese islands were depicted as distorted, oversized landmasses. One such enduring error was Lake Chimay—an imaginary lake placed around today’s Assam region, in the valley of China’s Yunnan province. It was believed that several rivers of northeast India, northern Myanmar, Thailand, Laos, and Yunnan originated from a single water body called Lake Chimay. First appearing in 1554, the lake continued to be reproduced on maps until the early 19th century, when it was finally understood to be nothing more than a cartographic myth.

Yunnan province borders the northern reaches of Myanmar, Laos, and Vietnam and lies roughly 200 kilometres from India’s closest village in Arunachal Pradesh. Rivers such as the Brahmaputra, Irrawaddy, Salween, Dharla, Mekong, Red River, Chao Phraya, along with several others in the Upper Assam valley and Myanmar’s Kachin State, all flow through this broader region. For centuries, it was believed that this vast imagined lake was the source of all these rivers. The first cartographer to map it was Giacomo Gastaldi in 1554—an Italian cartographer who worked with Ptolemaic traditions and relied heavily on accounts from European and Asian travellers. The practice continued, with successive maps reproducing this fictitious lake and adding towns and river names that appear almost comical in today’s context. A map dated 1705 by Guillaume de L’Isle marks rivers named Laquia, Caipoumo, Casa, and Asa. While it is difficult to identify these precisely today, the Brahmaputra, Irrawaddy, Dharla, and Chao Phraya were believed to originate from this lake. The Brahmaputra, or Tsangpo, rises from the Angsi Glacier near Lake Mansarovar and Mount Kailash in Tibet; the Irrawaddy originates in Myanmar’s Kachin State and drains into the Andaman Sea; the Dharla flows from the foothills of Sikkim and joins the Brahmaputra in northern Bangladesh as the Jamuna; and the Chao Phraya flows from Nakhon Sawan in Thailand and empties into the Gulf of Thailand. European cartographers had not traversed or mapped the Himalayas or the regions east of them and therefore made this erroneous assumption. In reality, none of these river sources are even remotely close to one another, making the eventual collapse of the Lake Chimay myth inevitable.

The reality behind Lake Chimay began to emerge through 17th-century Jesuit missionaries during their journeys to spread Christian teachings in China and Macau. In 1685, when Aurangzeb ruled Mughal India, the Kangxi Emperor (Shengzu of Qing) ruled Qing China, and King Narai ruled Ayutthaya in present-day Thailand, a French Jesuit missionary, Father Guy Tachard, discovered that the size and position of Siam were not as European cartographers had assumed. Mapmakers had placed Siam about 24 degrees too far east—a displacement of nearly 2,500 kilometres. When Tachard reached Siam, he realised that Asia was significantly smaller than it appeared on European maps. This revelation made it impossible to reconcile the supposed position of Lake Chimay, and although Tachard did not explicitly deny the lake’s existence, it no longer fit within his geographical understanding. Earlier Jesuits, such as Martino Martini and others, had already noted multiple variations in the lake’s supposed outlets and argued that rivers like the Red River and the Chao Phraya had different sources. Such observations began to sow doubt among Europeans about the lake’s existence and accuracy, though it continued to appear on maps with conflicting information about the rivers flowing from it.

Guillaume de L’Isle was among the first to seriously question the authenticity of Lake Chimay in the early 1700s, though he continued to depict it on his maps. By the 1730s, however, Jean-Baptiste Bourguignon d’Anville—another French cartographer—accurately mapped Tibet, Yunnan, and the entire river system of the region, leaving no place for Lake Chimay. By the early 19th century, the lake had disappeared entirely from European maps. The mythical lake had a long and curious life—imagined by Europeans and ultimately dismissed by them. Below is a recreation of Guillaume de L’Isle’s 1705 map depicting Lake Chimay.