Britain's Prince Charles wowed tourists, viewed monuments, addressed ocean pollution and got special gifts from the National Archives on Wednesday during his US goodwill visit with his wife Camilla.

The four-day visit by the Prince of Wales and the Duchess of Cornwall aims to boost British-American partnership in such areas as climate change and encouraging corporate social responsibility.

The 66-year-old-heir to the British throne, who has made the environment a special concern, called in a speech for stemming the flow of plastic waste into the world's oceans.

He said that a study has estimated that if nothing is done, by 2025 there will be a ton of plastic waste in the sea for every three tons of fish.

"Given all this, it seems to me, as I am sure it does to all of you, that something must be done urgently to stem the tide of plastic entering the oceans," the prince said during a conference of his International Sustainability Unit and the Global Ocean Commission.

During the first full day of their visit to the US capital, Charles and Camilla were swarmed by delighted tourists at the Lincoln Memorial and the Martin Luther King Jr. Memorial.

The royal couple worked the crowds with handshakes and hellos, with Camilla wearing a Bruce Oldfield embroidered gray-and-black dress and coat against a late-winter chill and stiff breeze.

At the National Archives, Charles viewed a 1297 edition of the Magna Carta, widely viewed as one of democracy's founding documents, and the US Constitution and the Declaration of Independence.

Charles burst into laughter when Archives officials presented him with a telegram sent from the US Embassy in London to the US Secretary of State in 1957, when the prince was 8.

The telegram asks about "engine specifications" for the prince's "gifted midget car". so that it could be ready for him when he returned home from school.

Charles also was given a 1931 patent submission by his relative, Lord Mountbatten, for a polo mallet.

The royal couple made a stop at Mount Vernon, the country estate of the first US president, George Washington. They will visit the White House on Thursday, the first such visit by Charles since May 2011.

Charles is due to receive a leadership award on Thursday from the International Conservation Caucus Foundation. The couple travel on Friday to Louisville, Kentucky.