There aren't any theme parks in Alaska. (It probably has something to do with the short summer season -- and the relatively few number of people who live in the state.) But, there is an indoor water park.
H2Oasis Indoor Waterpark
Alaska's only indoor waterpark is open year-round-- even when it's 30 degrees below zero outside. Features a Master Blaster uphill water coaster, a wave pool, and a lazy river.