Moran State Park on Orcas Island is an amazing place to camp. First of all, you need to take a ferry to get there, which is part of the adventure. When we visited Moran, we were living on San Juan Island, so the ferry ride was just 30 minutes. But if you leave from Anacortes, plan for more like 90 minutes for your ferry ride.
As a quick side note, while you are waiting in line at the ferry in Anacortes around May or June, if you have some time, walk over to Charlie's and get the halibut fish and chips. It is some of the best I've had, and I used to live in Homer, Alaska, a huge halibut fishing area, so I've had some really good halibut.
Anyway, back to Moran, there are 5 freshwater lakes within the campground, including one set up for swimming with public changing and rest rooms and a snack bar, and a nice "beach" area to sit out and watch the kids.
One of the highlights of camping at Moran State Park is hiking up Mount Constitution, which is really more of a walk since you can drive almost to the very top. From this lookout, which is the highest spot in the San Juan's, you can see all the way to Canada, get a view of all the San Juan's and surrounding islands, see the Cascade Range and even spot some big Washington cities. It's amazing.
My son had a great time casting with his fishing pole in the lake right next to our campground, although I don't think there were any fish at the time. I think certain times of the year are better than others. There are also non-motorized boats for rental, or bring a canoe or kayak and explore amazing and beautiful Moran State Park on Orcas Island.