There are octopi that are already pretty smart. Who knows what could happen in another billion years. Many sea animals, like sharks and eels sense or use electricity under water. So do we. If it's easier to build technology above the water, well then it's easier. But that would just mean it would take longer to develop under water. And make no mistake, it's the use of technology that interests you. So what might drive a species to technology? Well, with my octopi example, they might be encouraged to build shelters from predators. They then might be interested in tools to open shell fish or something to get at food sources. They then might want movable shelters. And so on. That's more or less how we did it. They won't have fire. Our technology and science has in many ways been 'fired up'. So they might investigate electricity first. Astronomy may take a long time. Lots of our solutions, like rockets, might seem unlikely for an underwater species. But rockets are pretty unlikely for us as well. And we have xray telescopes in space, despite the fact that we can't see xrays, and they don't make it to the ground naturally. I'd be hopeful that an underwater species could eventually make the transition.