Cherie Priest's Fathom
a battle between Elementals to save humanity and the humans who are "called into service" to help.
Arahab is a water witch, capable of manipulating oceans, lakes and even puddles. For millenia, she has plotted to awaken the Leviathan sleeping at the center of the earth. She's been searching for humans who could actually get down into the core to plant a 'call' totem and get things moving. So far, she has only found one human deemed capable of the task: Jose, a pirate who drowned himself to avoid capture. But he's tried once and failed, so Arahab's on the prowl for a deckhand.
Up on land, a farmgirl named Nia visits her spoiled cousin, Berenice, who is staying with her mom and stepfather on an island in the Gulf. When Berenice nearly drowns, she is taken by Arahab; Nia is swept up onto the shore and into the form of a statue. Workmen find her and leave her in the aunt's garden. The aunt flees town and slowly statue-Nia goes crazy trapped in her shell alone.
Enter Sam, a slightly bumbling insurance agent called by a possible buyer to inspect the grounds and a creature called Mossfeaster, who forms out of whatever earth-y matter is at hand (vines, dirt, rotting plants, other fun stuff) and is determined to stop Arahab. First, however, he has to save Nia before a group of local nutjobs have one too many midnight ceremonies around her and bring on the attention of something bad.
This is where I stop telling you stuff and you start reading instead.
Interested? Thought you might be.
Slightly deterred from diving or gardening? Sorta suspected that, too.
As always, hit me up with your comments!