A reader sends a shot above Fiesta Texas, the Six Flags amusement park in San Antonio (and one that would drive the bigoted Eric Cartman crazy):
From the air you can see the giant Texas-shaped wave pool and the massive parking lot. The photo was taken by me, John Matthews, from about 3500 feet MSL [mean sea level] from a friend’s Mooney [a type of single-engine plane].
I spent part of my early childhood in Stuttgart, Germany, where my mom was stationed with the U.S. Army, and some of my fondest memories were of the waterparks big in that area. The waterslides were much faster and more fun than the ones I’d seen in the States, and for the first time I experienced what a massive wave pool was like. A cursory history of wave pools suggests that my first encounter with one in Germany wasn’t a coincidence:
Wave pools go as far back as the 19th Century, as famous fantasy castle builder Ludwig II of Bavaria electrified a lake to create breaking waves. The first [swimmable] wave pool was designed and built in 1927  in Budapest, Hungary, and appeared in a Metro-Goldwyn-Mayer documentary about the city in 1938, as one of the main tourist attractions. Palisades Amusement Park [in NJ] had a salt-water wave pool during the 1940s. This was a huge pool whose waves were generated by a waterfall at one end. The pool in Point Mallard Park [in Decatur, AL] was developed in the early 1970s after Mayor Gilmer Blackburn saw enclosed “wave-making” swimming pools in Germany and thought one could be a tourist attraction in the U.S.
There’s also a fantastic video on YouTube purportedly shot in 1929 showing a wave pool in Munich (“This is the new kind of swimming bath that is becoming the rage of Germany,” the opening card reads):
As far as present-day superlatives, Siam Park City Water Park in Thailand is home to the world’s largest wave pool (video here) and the similarly named Siam Park (Tenerife) in Spain produces the largest waves—nearly ten feet tall (video here).