Do you have to have a reservation or do they have sites available the day you arrive

No you do not they have first come non reservable

If you want an electric and water site those are in loop one for sure you can make a reservation for those but the also have first come first serve sites that are just electric

They have walk ups available on a first come first serve basis.

There are some sites that are first come first serve mostly in loop 5

They do have sites first come, first serve

You have to make reservation. Very nice. Beach