Here's the full equation: https://en.wikipedia.org/wiki/Drake_equation
I also think that echolocation has potential to be equal or better to eyesight! Bats and dolphins do great with it, and I think that it's easy to think of echolocation as being a _visual_ stimuli, even though it's not lightwave-based.
I think the biggest hurdle for an underwater sentient species trying to become more advanced is the difficulties with tool-building. Simple stone tools could be made, but it becomes a lot harder to smelt iron and start doing metal-working.
Would they have to be underwater, though? They could use the sea surface, provided the atmosphere is not toxic to them.
I think due to their Water environment WHALE did not become the dominant spices on EARTH but Humans became .
https://en.wikipedia.org/wiki/List_of_animals_by_number_of_n...
By the way, the all-caps in your message makes your post kind of confusing, and it almost sounds sarcastic? I'm just letting you know in case English isn't your first language. :)