I’m a scuba diver and you can definitely harm regions of ocean with water pumps. It’s already happening in place where nuclear is being cooled. It’s already happening in ship yards.

It’s hard to speculate how it would happen at scale though because ocean science is real fucking hard and each location is vastly different. In populated places the damage would be very noticeable if not eventually catastrophic as ocean issues compound real fast as the ecosystem is much more fluid.

That being said I imagine there would be ways to deploy this safely (ocean is big, lots of boring dead space) but I dont have trust in us to find this way.