Not counting the ancient pools of a few select kings and rulers in places like Babylon and Rome, the history of residential swimming pools pretty much began in Southern California. Starting in the mid-1930s, newsreels and magazine photos of movie stars posing by their swimming pools sparked a trend, which became more popular during the post-World War II housing boom. By 1947, there were 11,000 pools in the United States. Things that can dictate the shape of your pool: lot size and available space, lay of the land, budget, meeting safety codes, your home’s architectural style, sun exposure, how you will use the pool and if you want an integrated or separate spa. Discover the basic pool shapes, with variations within each category. Hoxton / Astronaut Images / Getty Images  The focal point of the Donnell landscape design is a sculpture by Adaline Kent, which serves as an island in the center of the kidney-shaped pool.   A group of natural figure-8-shaped pools is at Sydney’s Royal National Park in Australia. The Figure Eight Pools are located in the southern portion of the park, near Burning Palms Beach. The pools form near-perfect figure 8’s on the coastal rock shelf. Although the platform and pools are hazardous to visit, pictures on social media have made the destination extremely popular. The site is safest to visit during low tide, but even then, there aren’t any lifeguards to make rescues or ensure safety.     Matt Henry Gunther / Getty Images