Eating a meal of nagashi somen requires a nimble hand with chopsticks. Otherwise your dinner could flow right past you.

Somen are white wheat noodles, which Japanese cooks serve cold or over ice during the summer. Typically, they’re boiled and cooled, then eaten with tsuyu, a sauce made from dashi soup stock and soy sauce. Common toppings include cucumber and sliced mushrooms. The Japanese have eaten somen since the eighth century, but they didn’t start floating the noodles down artificial rivers until modern times.

In the southern town of Takachiho, in 1959, the House of Chiho restaurant dreamed up nagashi (flowing) somen in order to capitalize on the pure, local spring water. In a tradition that continues today, staff fill long chutes of halved bamboo trunks with cold running water. Once they yell, “Ikuyo!” or “It’s coming!” they add strings of cooked noodles for diners downstream to snatch out of the current. At most establishments, a basket at the end of the waterworks catches slippery noodles, and the staff retrieves them for customers. But at the well-known Hirobun restaurant in Kyoto, what you catch is what you get, until red-dyed somen floats through and signals the end of the meal.

People in Japan will buy bamboo shoots to serve nagashi somen at home. But as an alternative, home cooks and restaurateurs can buy machines that spin noodles around circular basins or send them down miniature water slides that look like toys.

Still, the traditional style has a special appeal. In 2016, the citizens of Gose, in Nara prefecture, set the Guinness World Record for “longest distance to flow noodles down a line of bamboo gutters.” They built a working nagashi somen chute that was 3,317 meters (10,871 feet) long. Other record-breakers, meanwhile, have used high-pressure washing machines to power noodles to speeds that created actual waves.