Trivia: George Lutz denounced this remake, stating that it was complete drivel.
Trivia: During filming of the movie, strange supernatural occurrences happened on set. A lifeless body washed up on the shore by the lakeside movie set and actor Ryan Reynolds stated that many cast and crew began waking up at 3:15 a.m. This is the same time the Defeo murders occurred.
Answer: He sees the balloon, and instantly assumes his step-daughter is inside the boat house, and hence is in danger of slipping and drowning (or perhaps already in such a situation). He rushes straight out to get there as quickly as possible. Checking her room, or telling his wife would take up time, not to mention he is probably running on adrenaline.