The Inland Sea in Gozo, swim-through, cavern or cave?
I have done quite a few cavern dives or what could be termed as giant swim-throughs. But what is the difference between a swim-through, a cavern and a cave dive?
These are all overhead environments, that means that if you have difficulty in one of them then it is impossible to surface immediately. Sot you have to take care when you are inside them.
Swim-through
I have looked hard for a definition of a swim-through but I haven’t been able to find a concrete one that describes it. So here is my own:
A short underwater tunnel or passage that is big enough for a diver to pass through, however there are no passages leading off of the tunnel that a diver could take where he could get lost. It is also possible to see inside the swim-through without the aid of an artificial light source.
Cavern
A cavern is actually a cave but for diving purposes they make a distinction. Here is the definition of a cavern from the NACD:
The area of a submerged cave that is illuminated by natural sunlight is the cavern zone
There are no night dives in a cavern because the area in which you are allowed to dive (as a Cavern diver) must be illuminated without the aid of an artificial light source.
Cave
This is everything else. Basically no natural sunlight penetrates this area, it is completely black and without specialist training and equipment then you should not be diving inside them. At Christmas 2013, two inexperienced divers chose to try out their new diving equipment at the Eagle’s Nest. The Eagle’s Nest, in Florida, is considered one of the toughest cave dives in the world. For a lot of cave divers it is the Mount Everest of cave diving. Cave diving should not be attempted without the required training.
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So what is the Inland Sea in Gozo? The Inland Sea is a tunnel that leads from a small inland sea (surprisingly enough) to the Mediterranean Sea. It is quite dark, however it is possible to see day light. There are some small passages that lead off the tunnel but they either quickly lead to dead-ends or bring you back into the main tunnel. It is also possible to surface in the tunnel as it is not fully enclosed, but it is highly recommended that you don’t. Boats regularly take passengers from the Inland Sea outside and around to view the Azure Window and the Blue Hole. So is it a swim-through, a cavern or a cave? It’s a tough one to call. I think I would have to say that it is a giant swim-through.
Jump - Sail - Dive 
What about swim throughs that are not closed over head but are still too small or restrictive to surface. For example, while diving in Honduras, the reef gave a sort of natural ravine/canyon/swim through where we could all fit easily through, however even though above us was open, it was far too small for anyone to surface through in the event of a problem. I’m not sure if all swim throughs have to be enclosed spaces.
That’s a good point. However, I never said that a swim-through had to be an enclosed space, but if you do not have direct access to the surface (as you did in Honduras) I would class that as an enclosed space: you have to either continue to the exit or turn around and return to the entrance if you experience a problem.
When you were in Honduras and passing through the swim-through you were unable to reach the surface directly, even though you could see it. In my mind that means that it is an overhead restriction, which makes it an enclosed space.
We have just dived at the Poor Knights in New Zealand and there are some amazing caves and swim throughs there. Highly recommended if you are in this part of the world! http://anzacsailing.com/2014/04/28/upper-north-island-of-new-zealand/
Looks awesome! Thanks for the tip.