Led by NGOs like Surfrider Europe Foundation and the French branches of the World Wildlife Fund or Tara Ocean Foundation, Greenpeace Paris and Sea Shepherd, the marchers, as many as 2,000 according to the organisers, demonstrated along the Canal Saint Martin in the north-east of Paris.
"Oceans should be central to the climate, biodiversity and pollution debate," according to Surfrider Europe.
One of the calls was for more financing to combat marine pollution and to protect oceans in general.
Although the organisers are centrally concerned about serious threats to the environment and the urgent need for governmental and citizens' action, Saturday's event was full of imagination. Demonstrators wore blue, associated with the colour of the oceans, painted their faces and carried cuddly whales.
Never too young or too old to learn
Unesco's Intergovernmental Oceanographic Commission as well as the Ocean and Climate Platform held a day of lectures at the agency's headquarters in Paris.
A recent World Wildlife Fund study showed that France, with its approximately 5,000 kilometres of coastline on three different bodies of water, is one of the worst plastic-in-the-sea polluters.
Oceans are part of the solution
The role of oceans in climate and climate change was one of the major points under debate at the Climate Change conferences, COP21 in Paris and COP22 in Marakkech.
French coasts rise to the occasion
Elsewhere in France, on its Atlantic Ocean west coast, resourcefulness and creative thinking went into organising many events to mark World Oceans Day.
From sustainable seafood cocktail receptions to literature or video-clip competitions and dance shows, scientific and educational institutions like the Nausicaa Aquarium in Boulogne-sur-Mer in the north-west of France did their best to attract more attention on the day and over the weekend.
Even the French Riviera resort of Cannes mobilised for the environment with local and national marine environment organisations. They held talks, debates for all ages and screened a documentary film called, Meditéranée by Joseph Espla to help convince the public of their role in maintaining their beautiful, resource-rich and fragile marine and ocean ecology.
In spite of efforts to improve awareness in recent years, one regular diver said "coffee cups, water bottles and plastic bags can be found at all depths in the sea when diving off the French Riviera."