Estuaries face heightened vulnerability due to global changes, including frequent intensified flooding from high-intensity rainfall events, which induce sudden changes in environmental parameters. While estuarine organisms thrive in fluctuating conditions, their responses to intense and prolonged stressors may vary. Furthermore, the combined effects of stressors (e.g., decreased salinity and pH, increased turbidity) encountered during floods have rarely been studied on invertebrates under controlled conditions. Consequently, we evaluated the sensitivity of three dominant mollusk species (Littorina saxatilis, Macoma balthica, Mytilus spp.) to spring floods conditions. During 5 weeks, we exposed specimens to a 12-level gradient of exposure to periodic freshwater injections ranging from 0 to 9 days, under both control (salinity 0, pH 8.1, suspended sediment 0 mg L-1) and spring flood conditions (salinity 0, pH 5.7, suspended sediment 325 mg L-1). Mortality, growth and shell wear were measured after 2.5 and 5 weeks. For each species and sampling period, we used mixed linear models with two fixed factors: treatment (two levels, "control" or "spring floods") and hypoosmotic stress period (12 levels). Breakpoint analyses were used to identify sudden changes in each significant regression. Spring flood conditions amplified the negative impact of freshwater exposure on the mortality and induced greater shell wear of all species. Additionally, species-specific vulnerability levels were detected. Extreme events could therefore be key factors determining species distribution and functioning of estuarine ecosystems. Our study underscores the need to consider ecologically relevant combinations of environmental factors representing the complexity of natural conditions.