FWIW, one of my favorite Cozumel dive sites is Colombia Shallows where the average depth is about 20 feet. It's definitely a real dive.
Gordon,
Wow, we agree once again. I love that dive as well. I love to get Columbia Deep or Marricabo in first and then do a quick jump over to Columbia Shallows for great marine life and light. You can dive forever and get great photos with ambiant light. For some reason many dont believe that a 20 or 25 ft dive is worth doing. IMO when it comes to CS its just not true. There are three huge Parots that hang around there and have for sometime. We saw them again in Nov..