The coordinates mark the starting point of your dive. It is the jetty to a local restaurant and dive center, where you can probably lent some dive equipment, if needed. The shop owner is not informed about the cache - so you might keep this deep secret. It's possible to dive within the bay, but please be aware of maritime traffic on the water surface.
Starting from the given coordinates you have to dive in south direction (180°) for approximately 25 m. You will find a big cube made of concrete, with buoys attached. From here you have to follow the anchor chain for serveral meters to its end. Here, you will find the cache... or better our secret word. Please remember this secret word!
If you did not spent too much air looking for the cache you can extend your dive towards west (270°) to reach the opposite side of the bay.
As a logbook doesn't seem to be appropriate ;o) you have to send you entry to an email adress consisting of the secret word and the name of the cache:
_ _ _ _ _ _ _ _ deepsecrets@gmail.com
You will receive an automatic reply, if the secret word was correct.
Have a nice time exploring the bay of Tratinska.