Saltcrop

From the acclaimed author of The Stardust Grail comes the epic tale of two sisters who sail across oceans to find their missing third sister—and Earth's environmental salvation.
In Earth's not too distant future, seas consume coastal cities, highways disintegrate underwater, and mutant fish lurk in pirate-controlled depths. Skipper, a skilled sailor and the youngest of three sisters, earns money skimming and reselling plastic from the ocean to care for her ailing grandmother.
But then her eldest sister, Nora, goes missing. Nora left home a decade ago in pursuit of a cure for failing crops all over the world. When Skipper and her other sister, Carmen, receive a cryptic plea for help, they must put aside their differences and set out across the sea to find—and save—her. As they voyage through a dying world both beautiful and strange, encountering other travelers along the way, they learn more about their sister's work and the corporations that want what she discovered.
But the farther they go, the more uncertain their mission becomes: What dangerous attention did Nora attract, and how well do they really know their sister—or each other? Thus begins an epic journey spanning oceans and continents and a wistful rumination on sisterhood, friendship, and ecological disaster.