Jiang and Georgakopoulos conducted a study of the EM wave propagation in
fresh water for frequencies between 23 kHz and 1 GHz. This work presents
two analyses on electromagnetic waves. On one hand, the authors measured
the transmission loss given by the reflection at the air-water interface
and, on the other hand, they analyzed the propagation loss inside the
water due to its physical properties. They conclude that the propagation
loss increases slowly for frequencies up to 1 MHz, while it remains
constant between 1 MHz to 100 MHz and then increases dramatically for
higher frequencies. In addition, the total loss in the 3-100 MHz
frequency range, for a depth of 1 m, is from 10 dB to 45 dB smaller than
the loss in lower and higher frequencies. Finally, they tested a
half-wavelength loop antenna operating at 100 MHz inside fresh water and
they concluded that a diameter of only 5.3 cm is needed for the antenna.