Around 500 protesters marched across Lisbon on Wednesday, taking part in what they called a "Blue March" to attract the attention of world leaders and decision-makers to ocean preservation.
Organised by over 200 local and international groups, the protest happened just a few kilometres away from the venue where the United Nations Ocean Conference was taking place.
The five-day UN global event is gathering officials and scientists from more than 120 countries.
The UN is hoping the conference will bring fresh momentum to the protracted efforts for a global ocean agreement that covers conservation efforts on the high seas.
The conference is also expected to reaffirm and build upon some 62 commitments made by governments at the previous summit in Nairobi, Kenya, in 2018, from protecting small island states with ocean-based economies to sustainable fishing and combatting warming waters.