The Big One is a large, dark blue wave of water with a face and tongue made of water. It once smiles and eats Patrick's surfboard.
If one wants to live after surfing The Big One, they must make at least one sacrifice. Objects sacrificed to The Big One include Patrick and Squidward's surfboards, Cashy (which is later returned), and Jack Kahuna Laguna (which is later returned).
In every year ending in -009 (e.g. AD 1009) during the alignment of the planets in the solar system, The Big One appears. The Big One will next appear in 3009, 1000 years after the previous one (2009).