Jake Gyllenhaal took a shirtless dip in the water with his sister, Maggie Gyllenhaal, on the North Shore in Oahu earlier this week. Jake and Maggie were hanging out in Hawaii for their father Stephen Gyllenhaal's wedding. Jake showed off his fit form as he continued their island vacation, and that six-pack is a welcome Summer sight. Jake has been focused on staying in shape for his role as a police officer in End of Watch, going on jogs with his costar Michael Pena and his brother-in-law, Peter Sarsgaard, and paying visits to the gym. Maggie threw on a strapless swimsuit to hit the beach with Jake, though her husband, Peter, isn't along for the family trip due to his Green Lantern press duties, which have taken him to Spain and Germany in the last week. Jake brought his sexy tan back to LA after the weekend, and he was spotted visiting a friend in the city yesterday.