Elephant gathering at Minneriya national park Sri Lanka......(CNN) -- Poachers have decimated elephant populations across Africa and parts of Asia, killing thousands of animals for their revered ivory. Yet in Sri Lanka, home to some 7,000 wild Asian elephants, a different, more hopeful story is playing out. It's a story that's attracting truckloads of tourists from around the world to witness a stunning wildlife spectacle, simultaneously raising concerns among conservationists about how increasing numbers of visitors may be impacting the large mammals. In north-central Sri Lanka's Minneriya National Park, hundreds of elephants travel each year to the shores of an ancient reservoir built by a king more than 1,700 years ago. They've made the trip for centuries, coming from across the region to bathe, mate, socialize and, most importantly, to feed as part of an annual event known as "The Gathering." During the dry season (July through early November), the water in the reservoir recedes. In its place, lush green grasses grow, providing a veritable feast for the hungry pachyderms. Between meals, the elephants head into the reservoir, spraying themselves with the shallow, muddy waters to create one of the world's biggest pool parties. "Where else you can get so close to so many wild elephants at once?" asks James Thomas, a lawyer visiting The Gathering from Melbourne. "Watching massive herds of elephants bathe as the sun sets over the nearby mountains is an experience I'll never forget."