Is that the level where it's at the very bottom? I found that if I slowly swam down then either tried to swim sideways and up I got into the switch! Those water levels are hard lol

I also found the secret level in the frozen level ( can't remember which level - 34 or 35?) it's up the top running to the left and it's behind a lot of ice ( I used a couple of bombs) but I found that I had gotten into it and found the stuff but it doesn't come up on the main screen that I have found it!

The secret level is on 25