River Marked (Mercy Thompson, #6) by Patricia Briggs

In the sixth novel in the #1 New York Times bestselling series, coyote shifter Mercy Thompson and Alpha werewolf Adam finally reach the alter. But when they make the Columbia River their honeymoon destination, their newlywed bliss turns into a fight for survival...
 
Being a different breed of shapeshifter—a walker—Mercy can see ghosts, but the spirit of her long-gone father has never visited her. Until now. An evil is stirring in the depths of the Columbia River—and innocent people are dying. As other walkers make their presence known to Mercy, she must reconnect with her heritage to exorcise the world of the legend known as the river devil.