EDITOR'S NOTE: This year, the U.S. National Park Service turns 100. American's 28th President, Woodrow Wilson, formed the National Park Service in 1916 to "protect the wild and wonderful landscapes" in the United States. Today, the National Park Service protects over 400 parks and historical sites from coast to coast. Every week, VOA Learning English will profile one of the sites within the National Park Service.

The West Potomac Park in Washington, DC, lies just west of the National Mall. It is home to some of Washington's most iconic sites, like the Jefferson Memorial, the Martin Luther King, Jr. Memorial, and the Tidal Basin.

But, the park's most famous attraction? Cherry blossoms.

Thousands of cherry trees bloom around the waters of the Tidal Basin, which reflect the trees' images. The basin was created in the late 1800s to prevent the Potomac River from flooding.

These pink and white flowers serve as a symbol of international friendship. The original cherry trees were a gift from Japan.

On March 26, 1912, more than 3,000 cherry trees arrived in Washington. Most were planted around the Tidal Basin. But cherry trees were also planted near the Washington Monument and the White House.

Mike Litterst is a spokesperson for the U.S. National Park Service. The park service maintains West Potomac Park, and helps protect the cherry trees.

"It's this wonderful gift that's over 100 years old now that, if you will, it's the gift that keeps on giving. The 1912 gift from the people of Japan has grown to this 3,800 trees."

The cherry blossoms also serve as a symbol of the beginning of springtime. The trees burst with colors of soft pink and white.

"The blossoming of the cherry blossoms every spring is sort of the great springtime celebration, not only in the District of Columbia but throughout the United States."

Every year, Washington celebrates the arrival of spring with a two-week Cherry Blossom Festival. More than 1.5 million people from around the world visit the nation's capital during the festival. They all hope to see the cherry trees at their "peak bloom."

Park officials define "peak bloom" as the period when 70 percent of Washington's most common cherry tree variety -- the Yoshino trees -- are blooming. Yoshino cherry trees are one of 12 types of cherry trees in Washington. Peak bloom lasts several days each year.

Experts begin making peak bloom predictions in February. Visitors make their travel plans to Washington based on these predictions.

Some years, the early guesses are correct. Last year, officials correctly predicted the peak bloom six weeks in advance.

But this year, unpredictable weather in March in Washington has made guessing the "peak bloom" difficult. "Peak bloom" dates have changed many times.

"We use a combination of natural indicators - we look at the trees, what are the trees telling us - we look at the historic record, but primarily what we are looking at is the forecast temperatures as we go from February and into March. This year the forecasts were sort of all over the place, which caused us to change considerably."

Carl Feasley and his family visited the Tidal Basin one day before the 2016 peak bloom was set to begin on March 23. It was his first time to see the cherry blossoms.

"We're coming from Buffalo, New York, where it's been winter for, even a mild winter this year, but winter for the past 5 months or so, or so it seems. It's just nice to be out in the sunshine and see evidence of spring all over."

Virginia Walsh is a Washington, DC local. She said she comes down to the Tidal Basin several times every spring to enjoy the cherry blossoms.

"I always try to come early, the peak, and then a couple days later. It's normally three times a year. I just love this place."

The cherry blossoms may signal the start of spring in Washington. But they have also become a worldwide symbol of Washington itself.

Bo Wen moved to Washington from China seven years ago. He comes to the Tidal Basin every year during the Cherry Blossom Festival.

"It's just famous. Everywhere you can see like Washington DC Cherry Blossom Festival, on like Twitter and Instagram. In the world everywhere, people just know that."

I'm Ashley Thompson.

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festival - n. a special time or event when people gather to celebrate something

peak - adj. at the highest point or level

bloom - n. a time period in which a plant has many open flowers

unpredictable - adj. not capable of being known before happening

indicator - n. a sign that shows the condition or existence of something

all over the place (idiomatic) - not well organized or carefully considered

considerably - adv. by a large amount or to a large extent; greatly.