Water transport in an operating PEM Fuel cell remains a significant research challenge. Many models exist, but experimental data remains uncommon. Thus model verification has not occurred. In this work, magnetic resonance imaging was used to study the spatial distributions of water in an operating hydrogen fuel cell. New insights were gained, such as the observation of wavy-stratified water flow pattern, instead of slug flow. Also, the water waves become 'stuck' in the flow field channels, apparently due to small defects in the flow field channel walls and bottom. These observations have not been previously predicted or reported.