alt Hacker NewsOceans have salt. Saltwater is bad for electronics beyond normal water. You also need a sufficient level of water depth otherwise it'll warm to surface temperature. It also needs to be price-competitive with traditional evaporative cooling.
Toronto is the textbook example of this working. It's on a freshwater lake that is deep relatively close to the shore, and the downtown has expensive real estate blocking traditional methods.
https://en.wikipedia.org/wiki/Deep_Lake_Water_Cooling_System
In a proper 2-loop cooling system, the primary loop (with direct electronics contact) and secondary loop (with seawater/external cooling source) are hydraulically isolated by a heat exchanger. The salt water or whatever never gets anywhere near the electronics.