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... the ocean might simply be good at blocking transmissions.
The ocean isn't just good at blocking transmissions. It's ridiculously good at blocking radio waves. If you work the math on this page, you can see that your basic WiFi transmission (at 2.4 GHz) will experience an attenuation of almost 1700 dB/meter! At that rate you'd get far less than a millimeter of penetration.
Even the lowest frequency short wave bands (1.8 MHz) get 46 dB/meter attenuation. It starts to get possible to receive RF when you get down in the kHz range but of course, your data rate goes to hell.
For underwater communications under a couple hundred meters or so you can use an acoustic modem. Even then, your best data rate is going to be on the order 2400 baud or less.
If you want high speed underwater communications, you gotta use a cable.