"Let us work together to create new waves of action for ocean sustainability - for people and the planet," Ban said in a message marking the Day.
"From trade to food to climate regulation, the oceans are integral to all of humanity. This is particularly so for coastal dwellers whose income and culture are irrevocably bound to the sea," the UN chief said.
"If we are to fully benefit from the oceans, we must reverse the degradation of the marine environment due to pollution, over exploitation and acidification," he said, urging all nations to work towards that end, including by joining and implementing the UN Convention on the Law of the Sea, the broad based treaty governing the world's waters, often referred to as the "Constitution of the oceans".
This year's theme for the Day is 'Oceans and People'. The United Nations has planned a host of activities organised by the global body's Division for Oceans and the Law of the Sea.