Do we have to have a reservation or is it first come first serve??

For camping you need a reservation. Keep checking the reservation website because people drop their reservations all the time. For day use you don't need a reservation.

You should definitely have reservations.... And you'll still wait hours to get checked in.

Only for camping you need a reservation. Reservation is not required to visit the park for the day.

We went on a Tuesday. We got there at 9 had wait a hour to get in. Lots vehicles where already lined up. So get there earlier