Drowning risk factors may be identified by comparing drowning incidence rates for comparable at-risk populations but precise methods are lacking. To address this knowledge gap, an ecological study extrapolated crude time-duration exposure to water for a specified at-risk sample of surf bathers to estimate the bather population for all wave-dominated beaches in Victoria, Australia, over a four-year summer season period. An incidence rate was calculated using surf bather drowning deaths frequencies matched for time and location. For the sample, 47,341 hours of surf bathing were estimated from 177,528 bathing episodes. Generalising these results to Victoria, the crude drowning deaths incidence rate in the summer season was 0.41 per 1,000,000 person-hours of surf bathing (95% CI 0.37–0.45). Further application of the method, particularly in open water settings, may be used to identify candidate drowning risk factors to advance drowning prevention strategies.