Over 150 divers from throughout Croatia and about 30 of their colleagues from Slovenia took part in the clean-up, removing dozens of bags of solid waste on both sides of the bay - in Piran, Savudrija, Veli Joze campsite and Kempinski beach.
About 20 children participating in the 5th International Children's Diving Eco-Patrol also made their contribution.
"Drives like this are praiseworthy and that's the direction we should all be going for the environment," said the Minister of Economy and Sustainable Development, Tomislav Coric.
The main objective of the drive was to clear the sea bed of waste as well as to draw attention to the global problem of sea pollution and raise public awareness of the importance of preserving the flora and fauna of the Adriatic Sea, Andreja Vedrina said on behalf of the organisers, Promocija Ronjenja.
"Projects like this contribute to the good neighbourly relations which Croatia and Slovenia have fostered for many years, while the clean-up drive itself contributes to preservation of the underwater world of the Adriatic Sea," Slovenian Environment Minister Andrej Vizjak said in a video message.