Corrosion - Cathodic Protection, page-4

ICCP generally require an transformer rectifier unit (TRU) to power the anode. And this TRU cannot be immersed in water, as it is an electrical equipment... which is why ICCP can be found installed on ships.

In my opinion, ICCP cannot be installed to protect the tethered buoy because there is no above water level structure to house the TRU. However... another innovative way that they can come up with is to utilize the electricity produced by the buoy itself to power the anodes to protect itself (we occasionally use solar power to power anodes in rural areas). Of course, there may be risk.