When visiting Lake Arrowhead, CA inbetween prime seasons, there isn't much to do. You can hike, fish, or boat (or day drink, I guess....but that wasn't an option for us). While we visited Lake Arrowhead in April 2010, we decided to take a boat tour of the man-made lake and hear a local's perspecitive on the area.
The Lake Arrowhead Queen Boat tour is the boat tour to take (I think it's the only one on the lake). The boat itself is a mini-river boat (minus the big waterwheel) and it seats about 30-35 people. It costs $16/adult and lasts about 50 minutes. On the ride, you get an interesting narrative on the creation of the lake, the dam, the entertainment industry's influence on the community and the celebs that live around the lake (Family Circus cartoonist, Patrick Swayze's old house, Sammy Haggar's old house, etc). It's a nice way to learn more about Lake Arrowhead and the community surrounding it, and a rather pleasent way to spend an hour.