This Thursday marks the 100th anniversary of the National Park Service, and the celebration comes with a little bit of freedom.

For four days this week - from Thursday, Aug. 25 to Sunday, Aug. 28 - all entrance fees will be waived at the 124 national parks that normally charge them.

In Oregon, that means free admission to Crater Lake National Park and Lewis & Clark National Historical Park. In Washington, it includes Olympic and Mount Rainier National Parks, as well as Fort Vancouver.

Camping and other recreation fees will still be in effect for the celebration.

The fee waiving will also extend to state parks in Washington, which will not require a statewide Discover Pass to visit park sites on Aug. 25 in honor of the park service centennial.

This month's national park free days are four of 16 offered in 2016, but are the only ones offered in the summer. The biggest stretch - a full nine fee-free days - came back in April for National Park Week. Two more are slated for the rest of the year: Sept. 24 for National Public Lands Day and Nov. 11 for Veterans Day.

--Jamie Hale | jhale@oregonian.com | @HaleJamesB