The following are known Action Replay Codes for Hydro Thunder on Nintendo 64 (N64).

Device Compatibility: Action Replay & GameShark

Master Code – Must Be On
f124ffa02400

Always 1st Place
812c4c960001

Infinite Turbo
802c4c9d00ff

Enable All Tracks
812b5c940101
812b5c960101
812b5c980101
812b5c9a0101
812b5c9c0101
812b5c9e0101
812b5ca00101

Enable All Boats
812b5ca20101
812b5ca40101
812b5ca60101
812b5ca80101
812b5caa0101
812b5cac0101
812b5cae0101