Saffron - Book One of The Neptune Chronicles by Vic Warren

"Saffron" tells the story of Jamie Edmondson, a passionate environmentalist and diver whose restless heart is tested when he’s called to investigate strange marine mammal sightings off California’s Big Sur region and discovers a race of underwater humans. “Saffron” is a powerful story built around the strong emotional hook of the destruction of the world’s oceans. When the Neptunes (as humans call them) surface, Jamie realizes that their race is slowly dying and their youth are born deformed due to extreme ocean pollution. The Neptunes develop a sincere bond with their human friends, hoping things will change, until they realize that they are going to be exploited by political and corporate powers.