Highly recommend this campground if you are someone who loves water.  The falls are a must see and it's a beautiful sound to fall asleep too.  Water up in the mountains never gets that warm,  but I tend to notice around June to end of August the water is at its warmest.  After a long hike around the mountains, you won't even notice the temperature.  You'll be extremely happy to just jump right in!  As a side note- you can camp at Elk Falls (FOR FREE) instead of going to Linville Falls Campground.  I couldn't find that on this website, but I highly recommend that site over this over, if you are someone who likes a more secluded, off the regular trail camping.