The Neptune Project by Polly Holyoke

This first book in The Neptune Trilogy is one of my favorite books, the first time I read it was when my friend loaned it to me. Nere Hanson loves swimming in the sea and diving with her dolphin friends. But then her mother—who is a scientist—changes her, she makes it to where Nere, her friend Robry, and Former-Friend Lena, can breath underwater, it turns out they were genetically altered to live in the ocean—permanently. Now they’re supposed to head to Nere’s father’s colony he’s building for kids like them, called Safety Harbor. Nere and her friends meet Dai, Kyel, Bria, Tobin, Thom, and Ree, who were also designed to live in the sea. They are all part of The Neptune Project. Nere faces everything from giant squid to sharks. Then the ultimate betrayal leaves her reeling right before they reach Safety Harbor.