Decibel level in water has a different measurement than in air! “The decibel is a relative unit of measure, not an absolute one. Confusion arises because relative intensities in water are referenced to 1 microPascal (µPa) whereas sound waves in air are referenced to 20 microPascals (µPa). The intensity of a sound wave depends not only on the pressure of the wave, but also on the density and sound speed of the medium through which the sound is traveling. Therefore, relative sound intensities given in dB in water are not the same as relative sound intensities given in dB in air.”
http://www.dosits.org/factsandmyths/ (#11)
For more detail:
http://www.dosits.org/science/soundsinthesea/airwater/
