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Talk about too close for comfort.

The National Park Service (NPS) is urging visitors to practice safe social distancing at parks that remain open during the coronavirus pandemic.

With the COVID-19 outbreak drastically disrupting daily life for millions of Americans, the great outdoors have become a welcome refuge for many. Inspired, Secretary of the Interior David Bernhardt temporarily suspended all park entrance fees last week to make it easier for people to get outdoors. The decision is effective until further notice.

Visitors watch the morning sun illuminate the Grand Tetons from within the Great Room at the Jackson Lake Lodge in Grand Teton National Park north of Jackson, Wyo. in this file photo. (AP Photo/Brennan Linsley,File)

Visitors watch the morning sun illuminate the Grand Tetons from within the Great Room at the Jackson Lake Lodge in Grand Teton National Park north of Jackson, Wyo. in this file photo. (AP Photo/Brennan Linsley,File)

However, visitors reportedly came out in such droves that three of America's most famous national parks — Yellowstone, Grand Teton and Great Smoky Mountains — closed their gates on Tuesday. According to The Associated Press, park authorities struggled to enforce social distancing measures and health safety recommendations from the White House and the Centers for Disease Control and Prevention (CDC)

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Tourists photograph Old Faithful erupting on schedule late in the afternoon in Yellowstone National Park, Wyo. (AP Photo/Julie Jacobson, File)

Tourists photograph Old Faithful erupting on schedule late in the afternoon in Yellowstone National Park, Wyo. (AP Photo/Julie Jacobson, File)

In another colorful example, though Joshua Tree National Park was formally closed to cars and campers over the weekend, swarms of hikers and bikers still ventured inside – which irritated locals, the New York Post reports.

Also over the weekend, the National Mall’s Tidal Basin and areas of Shenandoah National Park were closed due to congestion concerns and effective social distancing practices, TravelPulse reports. In Zion National Park, parts of the popular Angel's Landing trail have also been closed.

On Tuesday, the NPS took to Facebook to define proper social distancing and emphasize its importance in stopping the spread of COVID-19.

This file photo shows Zion National Park near Springdale, Utah. (AP Photo/Rick Bowmer, File)

This file photo shows Zion National Park near Springdale, Utah. (AP Photo/Rick Bowmer, File)

“Social distancing means avoiding large gatherings and maintaining distance (approximately 6 feet) from others when possible. While we're at it, let's remember to keep it 300 feet or more for larger wildlife,” a spokesperson for the agency said in a statement.

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“If you encounter a crowded trail-head or overlook, you're not practicing safe social distancing. Go elsewhere,” they continued. “If waving to your friend from six feet away, you're doing it right. If you're waving while standing next to a moose, you're not.”

A file photo of Yellowstone National Park's Lamar Valley near Mammoth, Wyo. On March 24, the NPS announced that Yellowstone and Grand Teton National Parks would be closed until further notice, and no visitor access will be permitted to either park. (AP Photo/Matthew Brown)

A file photo of Yellowstone National Park's Lamar Valley near Mammoth, Wyo. On March 24, the NPS announced that Yellowstone and Grand Teton National Parks would be closed until further notice, and no visitor access will be permitted to either park. (AP Photo/Matthew Brown)

Moving forward, Bernhardt has granted park superintendents the power to close facilities or otherwise modify operations in the fight against COVID-19, per guidance from the White House and CDC.

Other national parks that still remain open have closed shuttles, campgrounds, visitor centers and some trails to prevent the spread of the viral disease.

Hikers take a moment to take a selfie at the water side of the Y in the Great Smoky Mountains National Parks in this file photo. (Joy Kimbrough/The Daily Times via AP,File)

Hikers take a moment to take a selfie at the water side of the Y in the Great Smoky Mountains National Parks in this file photo. (Joy Kimbrough/The Daily Times via AP,File)

“The health and safety of our visitors, employees, volunteers, and partners is the priority of the National Park Service,” Bernhardt said in a March 17 statement.

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If planning a visit during the outbreak, the NPS asks that visitors check with individual parks regarding operations and hours. Further updates about the park service’s response to the coronavirus will be shared to its website.

The Associated Press contributed to this report.