Prince Charles told of Americans' 'fondness' for royals
US President Barack Obama has told the Prince of Wales of the "fondness" of American people for the Royal Family.
Mr Obama joked during a White House meeting that some "liked them much better than their own politicians".
Prince Charles and the Duchess of Cornwall met Mr Obama and Vice-President Joe Biden at the Oval Office.
The prince also visited an adult education school and took part in 10-pin bowling during this part of his four-day US "goodwill" tour.
Mr Obama and the prince last met four years ago when the king-in-waiting flew to the US a few days after the wedding of the Duke and Duchess of Cambridge.
Mr Obama told the prince during Thursday's meeting that it was "fair to say that the American people are quite fond of the Royal Family".
The prince replied: "That's awfully nice to know."
He was later presented with the exceptional leadership in conservation honour from the International Conservation Caucus Foundation.
During his acceptance speech Prince Charles highlighted his concern about the destruction of rainforests and the threat to endangered animals like rhinos, elephants and tigers.
"I repeatedly hear it said - as I am sure you do - that looking after nature is too costly; a barrier to growth and a danger to economic competitiveness," he said.
"So long as this perspective prevails, then I fear the destruction of natural systems will be seen as in some way rational and an unavoidable price of progress."
On Thursday Prince Charles also visited the Carlos Rosario International Public Charter School in Washington DC, which provides education and training for the capital's adult immigrant population.
He played 10-pin bowling during his tour of the city's US Armed Forces Retirement Home.
The six-lane bowling alley is designed to provide exercise for the veterans who live at the home.
Earlier in their tour, the royal couple visited monuments to Abraham Lincoln and Martin Luther King Jr and were joined by figures from the American civil rights movement, Jesse Jackson and Congressman John Lewis.
By Nicholas Witchell, BBC royal correspondent, in Washington
You'd think he was on the campaign trail, and in a very real sense he is.
By the time he heads home to Britain, Prince Charles will have made three major speeches about the need to do more to protect the environment.
In Washington, moments after receiving a prestigious award for "exceptional leadership" on conservation issues, Charles made his pitch - that when it comes to protecting the global environment, the world is looking to the United States to take a more robust position of leadership.
Charles uses language carefully. He is not by nature someone who resorts to hyperbole. He has an inbuilt aversion to the idea of the "sound bite".
So for him to use vivid phrases like "a perfect storm", and "truly exceptional challenges", in relation to the gravity of the environmental threat, is a measure of how keenly he feels about these matters.
He was similarly direct in his appeal to America's political elite. He called for "far-sighted" and "decisive" leadership on the environment.
This, one must suppose, was something he will have discussed with President Obama when he met him in the Oval Office earlier in the day. The president, of course, has been broadly supportive of the kind of action that Charles is advocating.
But Charles is well aware that there is a powerful lobby on the right of the political spectrum in the United States that is wholly unsympathetic to the environmental cause.
Charles isn't a politician, yet he is entirely committed to continuing the campaign that has already engaged his energies for so many years.
He was asked why he still cared so deeply about protecting the environment.
He replied that it would be odd if he didn't care when you consider how much there is to worry about .