Adi Ganga
Adi Ganga, also known as Tolly's Nullah, is a historic distributary channel of the Hooghly River that originates near Hastings in southern Kolkata, India, and flows southward across the city for approximately 75 kilometers, eventually connecting to the Piyali River and other waterways leading to the Bay of Bengal.[1][2] It served as the principal course of the Hooghly from the 15th to 17th centuries, functioning as a primary conduit for the Ganges' flow in the region.[1] Revered in Hinduism as a sacred extension of the Ganges, the channel holds religious significance, particularly due to its proximity to the Kalighat temple, one of India's major pilgrimage sites.[1] Historically, Adi Ganga played a crucial role in Kolkata's development as a navigational artery for trade and travel, documented in 16th- and 17th-century cartography and medieval literature, before colonial interventions reshaped its path.[1] In 1775–1777, Colonel William Tolly re-excavated and canalized portions of it to enhance drainage and connectivity to other rivers, transforming it into Tolly's Canal amid the East India Company's urban expansion.[1][3] This engineering effort integrated it into Kolkata's colonial drainage network, supporting the burgeoning metropolis until the rise of railways diminished its transport utility.[1] Over time, rapid urbanization, siltation, and neglect have severely degraded Adi Ganga, reducing its carrying capacity by 15–50% and converting much of it into an open sewer with elevated levels of biochemical oxygen demand, chemical oxygen demand, and coliform bacteria.[1] Encroachments, including metro construction in 2001 that embedded 300 pillars along its bed and displaced over 40,000 squatters, exacerbated its ecological decline, leading to heightened flood risks despite its ongoing role in the city's water balance.[1] Efforts to rejuvenate the channel persist, highlighting tensions between heritage preservation, urban infrastructure demands, and environmental restoration in one of India's most densely populated areas.[1]