Background The Sundarbans in India is a rural, forested region where children are exposed to a high risk of drowning due to its waterlogged geography. Current data collection systems capture few drowning deaths in this region.

Methods A community-based survey was conducted in the Sundarbans to determine the drowning mortality rate for children aged 1 to 4 years and 5 to 9 years. A community knowledge approach was used. Meetings were held with community residents and key informants to identify drowning deaths in the population. Identified deaths were verified by the child’s household through a structured survey, inquiring on the circumstances around the drowning death.

Results The drowning mortality rate for children aged 1 to 4 years was 243.8 per 100 000 children and for 5 to 9 years was 38.8 per 100 000 children. 58.0% of deaths were among children aged 1 to 2 years. No differences in rates between boys and girls were found. Most children drowned in ponds within 50 metres of their homes. Children were usually unaccompanied with their primary caretaker engaged in household work. A minority of children were treated by formal health providers.

Conclusions Drowning is a major cause of death among children in the Sundarbans, particularly those aged 1 to 4 years. Interventions keeping children in safe spaces away from water are urgently required. The results illustrate how routine data collection systems grossly underestimate drowning deaths, emphasising the importance of community-based surveys in capturing these deaths in rural low- and middle-income country contexts. The community knowledge approach provides a low-resource, validated methodology for this purpose.