to add to spiceycat's comments:
You pay the amount and charge to your room....about $211 including tax for up to five people. You can take out various boats and bicycles (not the surrey type bikes though). Your child must be at least 12 years old and 5' tall to take out a watermouse boat.
You get unlimited use though if they're busy they'll ask you to come back to the dock or bike rental shack every hour or so to make sure there's not a line. We've never had to turn in a bike or boat early due to others wanting to use them.
Also, some have posted recently that the plan is good for one week maximum now. When we used it this summer, it was good for length of stay, regardless of how long you'd be there. Even at a week, it's a good deal.
They provide life jackets and helmets for the kids (mandatory) .
It's a great value, all things considered.