Ambient noise measurements were carried out in shallow brackish water within a frequency range extending up to 70 kHz. The high-frequency spectral slopes become steeper above 10 kHz at intermediate and high wind speeds. This is because the start of the wind speed dependence shifts rapidly to higher wind speeds at frequencies above 13 kHz. A physical explanation for this observation may be the low proportion of bubbles in brackish water that are small enough to radiate sound above 10 kHz. Such bubbles apparently do not begin to develop in brackish water until high wind speeds are attained.