So what is it folks? What constitutes an acceptable loggable dive for purposes of continuing education where you have to show a dive log?
As many have said, you can log whatever you choose to log. But, to answer your specific question - for purposes of 'continuing education' - from a PADI perspective, here are some relevant items from the Instructor Manual definitions provided at the beginning of the 'Training Standards' section:
Logged dives: To credit a a logged dive for course requirements, the dive takes place in open water and specific information about the dive (date, time, depth, location, etc.) is recorded.
Since 'open water' is specifically required for qualification as a logged dive, another definition may apply:
Open water dives:
Open water is a body of water significantly larger than a swimming pool offering conditions typical of a natural body of water encountered by divers.
To address the point made in an earlier post about Nemo 33, it is worth noting that the definition also states:
There are certain sites (very large aquariums and specifically-constructed environments designed for recreational diving, for example) that provide conditions typically associated with natural bodies of water . . .
I think it can be said that Nemo 33 is definitely larger than a swimming pool, and qualifies as a 'specifically-constructed environment designed for recreational diving'.
And, the definition goes on to state:
. . . divers spend the majority of time at 15 ft or greater, and breathe at least 50 cubic feet of compressed gas, or remain submerged for at least 20 minutes.
The bottom line in all this: A loggable dive for CE purposes is an open water dive where you either spend a certain amount of time or breathe a certain amount of gas, while being submerged for most of the time at 15 ft or greater.
If I jump off a dive boat, to pull the anchor from a wreck at 100 ft, and spend 15 minutes in the water, I log the dive.