The Aquatic Adventures supplement states:
"If a PC fails her check by 5 or more while underwater (or doesn't spend any actions to swim, thus not even attempting the check), she sinks or rises based on buoyancy."
If I understand this right, any time a character forgoes making a swim check to full attack, he or she will sink at the end of the round. This DOES provoke attacks of opportunity.
Simultaneously, aquatic/water creatures can control buoyancy, and therefore can make full attacks without a swim check, avoiding the sink + AOO scenario.
Is this correct?