A major field experiment was conducted which obtained measurements of the attenuation and transformation of short gravity waves as they cross the windward edge of an offshore coral reef. Water level data were collected for over 3000 individual time series during a wide range of environmental conditions. At the innermost measurement site, which is located on the horizontal reef flat after the completion of wave breaking, the upper bound of significant and maximum wave heights is limited to less than 40% and 60% of the reef flat water depth, respectively. As with significant wave height, both the shape and energy level of the reef flat spectra are strongly affected by changes in reef flat water depth. For higher tide levels the spectra on the reef flat closely mimic the corresponding incident spectra. However, the attenuation is greater for both lower frequencies and higher-energy portions of the spectra. This causes the reef flat spectra to be broader than those measured windward of the reef. At lower water levels, considerable energy losses due to wave breaking and bottom friction occur. Most of the energy loss comes from the vicinity of the spectral peak, the energy shifts to harmonics of the peak of the spectrum can be seen. ¿ American Geophysical Union 1996