[jjmarr]

Oceans 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

[dpe82]

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.

[mschuster91]

The problem is, it's still in contact with something, even if it's just the secondary loop. Saltwater is not just incredibly aggressive against metal, the major problem with using it for cooling is fouling. Fish, mussels, algae, debris, there are a lot of things that can clog up your entire setup.

[millipede]

Saltwater comes in the air. Just being near it corrodes everything. Both stainless steel and bronze are very expensive. Even if things were made of corrosion proof materials, not everything can be, for strength reasons.