Two water days that are not interchangeable
A Gulf beach and a ticketed waterpark solve different wishes. Start at Isla Blanca Park for sand and open water, then keep Beach Waterpark on a separate day for slides, pools and a lazy river. This avoids asking everyone to carry beach gear through a second full outing.
Day one: Isla Blanca
Check Cameron County's current park information before driving to the south end. Decide on swimming from the latest National Weather Service surf forecast, not from the season name. Heat, thunderstorms, wind and rip-current risk can change the visit; a walk, picnic and swim are separate choices.
Day two: confirm that the waterpark is operating
Beach Waterpark is seasonal. Its official information page directs visitors to an operating calendar and says admission is required. Check your exact date and current ticket information before making this the centerpiece of the day. The park also states that it is no longer connected to the former resort or indoor waterpark, so do not follow outdated directions for those facilities.
Bring a backup for a closed or stormy day. Compare rainy-day activities, but verify how much of each attraction is indoors. The stops saved below do not include park admission, a cabana or permission to swim.