Naga fireballs (Thai : บั้งไฟพญานาค ; RTGS : bang fai phaya nak), also known as bung fai phaya nak or "Mekong lights" and formerly "ghost lights", are a phenomenon said to be seen annually on the Mekong River. Glowing balls are alleged to naturally rise from the water high into the air. The balls are said to be reddish and to range in size from smaller sparkles up to the size of basketballs. They quickly rise up to a couple of hundred metres before disappearing. The number of fireballs reported varies between tens and thousands per night. The phenomenon is locally attributed to phaya nak, a giant serpent (Nāga) said to live in the Mekong.