If I have a Gold Pass can I just show up for entry into either the water park or amusement park even if the waterpark is sold out?

You have to make a reservation

You have make reservations before going there

No you hace to have a reservatiob

You need a reservation, but with one reservation you can do both parks. In other words if one park is sold out reserve the other park wait an hour or so and go through the park to enter the other side. We did this and it worked😁

Yes you can!