Dive into Cachalot (1980) by Alan Dean Foster, a thrilling sci-fi adventure set in his Humanx Commonwealth universe. On the oceanic planet of Cachalot, human settlers coexist with bio-engineered, talking whales in a vast marine sanctuary. But when a mysterious threat endangers both humans and whales, a team of investigators must unravel the mystery. It’s a gripping blend of environmentalism, exploration, and action—all in the deep, alien oceans of a world unlike any other.