Aquamarine

Keegan's 1999 opus is set in the late 21st Century, when major land masses have been submerged by rising oceans and the Earth is a world of water. Russell is a hydrologist, based on the giant floating platform of Pacifica; his lover, Eric, is one of fifty Aquarians -- a new sub-species of human who can breathe underwater.

When the pair refuse an attractive offer for Eric's services on a suspicious salvage operation, Eric is kidnapped and a fast-paced intrigue starts to unfold on the "acorn principle" ... a small event turns out to be the key to a major war which would involve the whole Pacifica region