Remembered from a back cover blurb of a paperback while browsing in a used bookstore. The gist was human interstellar explorers discovering a completely ocean-covered planet and discovering an extensive underwater civilization. The overall feel of the novel was more or less hard sci-fi.
is it a Darkling Sea? the story is about first contact situation of humans with an extensive underwater civilization. It is on a water world, though it is an ice water world. It has been a while since I read the book and I don't remember much more about it, But the back blurb is
On the planet Ilmatar, under a roof of ice a kilometer thick, a team of deep-sea diving scientists investigates the blind alien race that lives below. The Terran explorers have made an uneasy truce with the Sholen, their first extraterrestrial contact: so long as they don’t disturb the Ilmataran habitat, they’re free to conduct their missions in peace.
But when Henri Kerlerec, media personality and reckless adventurer, ends up sliced open by curious Ilmatarans, tensions between Terran and Sholen erupt, leading to a diplomatic disaster that threatens to escalate to war.
Against the backdrop of deep-sea guerrilla conflict, a new age of human exploration begins as alien cultures collide. Both sides seek the aid of the newly enlightened Ilmatarans. But what this struggle means for the natives—and the future of human exploration—is anything but certain, in A Darkling Sea by James Cambias.