Dhaka’s rivers are severely polluted by daily discharge of untreated industrial wastewater, coupled with raw sewage, and solid wastes from the city’s 20 million residents. The ready-made garment industry, a key player in the country’s economic growth since the 1990s, significantly contributes to this environmental degradation which disproportionately affects low-income riverbank communities, who rely on the contaminated water for daily activities. We explore these social inequalities through observation of people’s river use behaviour across the dry and wet seasons. In densely populated slums, women and girls turn to the rivers for washing clothes and dishes to avoid long queues at shared water points. Meanwhile, men engage in washing and bathing near bustling marketplaces and boat terminals. During the monsoon, recreational activities like swimming and fishing increase, as the rising water levels create a deceptive appearance of cleanliness. Supported by monthly river quality monitoring, household surveys, and regulatory analysis, these ‘river diaries’ paint the complexities of water-society dynamics. Findings identify priority responses for the most vulnerable today with analysis to guide the sequencing and prioritisation of major investments in water treatment infrastructure in the coming decades.