Fluvial flooding is a recurring event in the Aie River basin in Assam, India. On August 14, 2021, floodwater breached a large stretch of embankment in the Bongaigaon District and inundated several villages. Using a cross-sectional design to conduct household surveys in February and March 2022, the study investigates responses six to seven months following the August 2021 flood disasters. The purpose of this study is to determine the prevalence and risk factors of four psychological health outcomes. Being flooded is strongly and adversely associated with each of these mental health outcomes. After adjusting for the potential confounders, the strength of the relationships is reduced to four times (adjusted OR 4.62 [95% CI 2.63–8.1]; p < 0.01) for PTSD, five times (adjusted OR 5.28[95% CI 3.38–8.26]; p < 0.01) for anxiety, and three times (adjusted OR 3.45[95% CI 2.24–5.33]; p < 0.01) for depression, and 21 times for comorbid PTSD, anxiety, and depression (adjusted OR 21.68[95% CI 7.38–63.74]; p < 0.01). The robustness of flood exposure is checked in an extended model. It includes variables that indicate the severity of flooding and various secondary stressors. The present study also explores the effects of ‘loss stressors’ such as crop loss, workday loss, livestock loss, and damage to infrastructure. Located in a resource-constrained setting, the effects of these factors add value to the study. Longer duration of floodwater in the house premise increases the odds of developing anxiety (adjusted OR 1.69[95% CI 1.04–2.75]; p < 0.05) and depression (adjusted OR 1.9[95% CI 1.15–3.12]; p < 0.05). Similarly, deeper floodwater inside the house increases the odds of depression (adjusted OR 1.87[95% CI 1.07–3.28]; p < 0.05). Among all the ‘loss’ stressors, damage to houses and the cost of repairing is significantly associated with PTSD (adjusted OR 2.04[95% CI 1.09–3.82]; p < 0.05), depression (adjusted OR 2.17[95% CI 1.22–3.87]; p < 0.01) and comorbid PTSD, anxiety and depression (adjusted OR 2.16[95% CI 1.07–4.36]; p < 0.05).