On the option screen. Hold down the R button, while holding press Up, Up, Down, Down, left, right, left, right, X, B, X, B.
The following case-sensitive codes should be used at the cheat screan:
PMeterGo
Max Out Performance Meter
TopBird
Opponents cannot knock you off your SeaDoo.
IBelieve
Race against a UFO in Time Trials
F18
Race Against an F-18 Jet in Time Trials
SEADOO
Race Against the Ghost of the Currently Selected Character
AllChar
Unlock all characters
Festival
Unlock All Ending FMV Sequences
LaPinata
Unlock All Wetsuits
Hobble
Unlock hard tracks with nomal AI difficulty