Depth (2015) by Lev AC Rosen [paperback]

In a near-future world where most of New York is under water and the mainland US is a bastion of censorship and religious extremism, Pl Simone Pierce plies her trade between the tops of skyscrapers and over the networks of bridges. A routine case helping an archaeologist search for artworks lost when the seas rose turns deadly as bodies start floating to the surface of the Manhattan waters.