Britain’s Prince Charles, long a champion of rain forests and sustainable agriculture, has a new environmental cause: combatting ocean trash.

“Something must urgently be done to stem the tide of plastic entering the ocean,” he said Wednesday at a conference on ocean debris, as part of a three-day tour of Washington.

“Having taken a keen interest in the state of the world’s natural environment for longer than I care to remember, one thing that has always struck me as being very odd has been the comparatively low level of attention that has been devoted to the condition of the oceans,” said Charles, the Prince of Wales and heir to the British throne.

“It is … utterly crucial that we do a great deal more to speed up the transition to a more ‘circular’ economy,” he said. “That is to say, one in which materials are recovered, recycled, and reused instead of created, used, and then thrown away.”

Charles spoke at a conference co-sponsored by an arm of the Prince’s Charities, which he leads, and the Global Ocean Commission, a consortium that makes policy recommendations on ocean issues, such as overfishing. About 125 scientists, economists, environmental activists, and plastic manufacturers met to consider possible solutions for keeping plastics out of the ocean.

Former Costa Rica President José María Figueres, co-chair of the Global Ocean Commission, also spoke at the conference, warning that “if we continue as we are, by 2025 we will have one ton of plastics for every three tons of fish in the ocean.”

The Prince’s Charities’ International Sustainability Unit, which Charles established in 2010 to take on environmental issues such as illegal wildlife trafficking and water, food, and energy security, added the problem of ocean debris to its portfolio last summer. Wednesday’s gathering was the charity’s first public meeting on ocean debris.

Although plastic debris has been accumulating in the world’s oceans since the World War II era, the amount and extent of its spread have been tallied only in the past few years. In addition to the large, floating garbage “patches” that accumulate in the five ocean gyres where currents converge, scientists have documented how pervasively plastic saturates all parts of the oceans.

Fragmented plastic the size of rice grains has spread throughout the deep ocean and become embedded on the ocean floor and in Arctic sea ice. It is also consumed by fish and other marine life.

Last December, for the first time, University of Georgia engineering professor Jenna Jambeck completed a count of how much plastic flows into the ocean every year. She found that in 2010, eight million tons of plastic was swept into the ocean from 192 coastal countries.

That figure is on track to double by 2025, Jambeck concluded, unless significant new methods to manage garbage in developing countries are devised to stem the flow into the sea.

Also on Wednesday, British Prime Minister David Cameron announced the creation of the world’s largest contiguous ocean reserve, setting aside 322,000 square miles (830,000 square kilometers) around the remote Pitcairn Islands in the South Pacific for special protection.

The new reserve is nearly three and a half times bigger than the landmass of the United Kingdom—larger than the state of California—and is home to a stunning array of sharks, fish, corals, and other marine life.