Here are some passwords for unlimited air. For unlimited air in a new game, enter "LIFEFISH" as your password.

The Undercaves LEVELSCT
The Lagoon SHARKFIN
Open Ocean KHDBVRIS
Ice Zone XRGQXRIX
Hard Water MAGLXRLM
Cold Water LNXHXRLB
Island Zone DVJLURIC
Deep Water OEWSURLC
The Tube FIVEPODS
The Machine ECCOFMLY