The potential for injury exists during the execution of a competitive swim start if an athlete contacts the pool bottom. The aim of the study was to provide vertical head velocities (VHV) at predetermined water depths when competitive swimmers perform worst-case scenario swim starts. A total of 22 swimmers performed starts from a standard starting block into a diving well with a water depth of 3.66 m. The starts were considered worst-case because the swimmers were asked to modify their typical start trajectory by traveling directly towards the pool bottom. VHV was 3.67 ± 0.66 m⋅s-1 at a water depth of 1.0 m and decreased to 1.67 ± 0.62 m⋅s-1 at a depth of 2.5 m. VHV was correlated (p < .05) with height and mass at the seven different depths evaluated. The potential for injury during worst-case starts existed at all depths measured. In terms of risk management for injury potential, there seems to be modest additional benefit to increasing water depth from 1.75 to 2.50 m as more than one third of swimmers would still have a 15% risk of catastrophic neck injury should an impact occur at 1.75 m water depth.