Technically you are only certified to dive under the same conditions in which you were trained. So if you did all your checkout dives in fresh water lakes, you are really only certified to dive fresh water lakes. However, it does not say that anywhere on your card nor will any Dive Boat Captain keep you from participating in an ocean dive. We can only recommend that any dive environments that you dive after your class that is different than what you were trained in, you should be accompanied by an instructor or at the very least a dive master. The only exception is if you are a Junior Scuba Diver (between the age of 10 and 14), then you must limit your depth to 60 feet and always dive with a certified adult.