Hi Matt359!
Many a player has gotten stuck in that underwater passage! Try using your smallest player as the lead and see if that helps. Try squirming around, sometimes that helps.
If you still can't get through, you have a choice -
You can skip it. What you get at the end of the tunnel is the snake idol which will give you access to the Book of Servants in the library. This book contains the responses you will need to make to the Naga Spirit when you perform the ritual. The responses can be found in the BEST TIPS thread.
OR
You can zip up your saved game and send it to either Xignal or myself and we'll see if we can get you past this tricky bit (we've both done this for other players). I seem to have difficulties with emailing back saved games to players of late - so Xignal would be a better choice but ask him first!
Wyv