The Kraken in the Lake by Annie Beth Rider

Kate needed a place to start over.
Her latest attempt at love had left her in financial ruins. Not only did her boyfriend gamble away her hard-earned savings, but he also managed to skip town before she could do anything about it. Kate was in desperate need of money, with no way to pay off the debt he had left behind.
When her sister swoops in to offer her a job, Kate is in no place to turn it down. She moves to northern Washington to become the property manager of her brother-in-law’s newly inherited lake house. What starts out as a simple job quickly turns into so much more.
With every day that passes, Kate discovers more and more secrets hidden within the lake house. It doesn’t take long for her to realize that she might not be the only person living on the lake. When a mysterious stranger appears in the water, Kate must decide if she is ready to open her heart again.
Is it possible for her to find love with someone from out of this world?