The mode-I dynamic fracture response of notched PMMA plates submerged in water was investigated. The experimental setup utilized was designed to study underwater crack propagation with the aid of visualization techniques to obtain quantitative and qualitative results. High-speed imaging and the method of transmitted caustics were used to complete the measurements. The main objective of this study was to determine the effect of surrounding water on the dynamic fracture behavior of samples as they were impacted. The properties measured to assess the effect of water were the stress intensity factor and crack speed in the initial stages of crack propagation. Experiments were also completed for samples surrounded by air for comparison purposes. Results showed that the presence of water had no effect on the fracture behavior of PMMA at strain rates of the order of 10 2 s -1 .