Bubbles were injected in a laboratory simulation of a breaking wave by an intermittent waterfall. A photographic method was used to investigate the size spectrum of bubbles in the plume generated by the falling water. Bubbles of diameter larger than 0.01 cm were measured. Snapshot obervations were assembled into residence-time weighted spectra. While the general features (log concentration versus log diameter slopes around -2) are consistent with other literature reports, a more detailed comparison shows considerable differences between seawater and freshwater populations. Bubbles were more numerous, smaller, and resident longer in the seawater plume than in fresh water. These results suggest that caution should be applied when gas fluxes measured in fresh water are used to infer gas fluxes in seawater when bubble-mediated gas transfer is likely to be significant. ¿American Geophysical Union 1995