It will be warm enough. In fact, it's warm enough right now.
The water is the same temperature no matter what, and that's cold. To get ready for your visit, take a cold shower, that's what it feels like, but after a few minutes you block it out. Start with your shower where you normally have it, nice and warm. Now slowly turn the dial until you've got it all the way on cold.
They do heat the water in the lazy river and they have warm showers.