Law enforcement officers arrested 76 protesters Thursday for trespassing on private property near the Dakota Access Pipeline construction site.

The arrests came as officials make headway cleaning up trash at campsites leftover from months-long anti-DAPL demonstrations. Officials wants the sites cleaned up to prevent an “environmental disaster.”

Morton County police believe the arrests will not hamper the cleanup efforts.

“Regardless of this incident it is our desire to continue the dialogue with tribal and camp leaders so that the camps continue to be cleaned and protesters leave prior to the flooding season,” Morton County Sheriff Kyle Kirchmeier said in a statement.

The arrests came after Democratic Sens. Maria Cantwell of Washington, Tom Udall of New Mexico, and Jon Tester Montana sent a letter to the Trump administration objecting to executive orders President Donald Trump signed okaying both the Keystone XL and DAPL pipelines.

“By ‘expediting’ this process and proceeding without appropriate consultation, the United States would be turning its back on its most solemn trust responsibility to the Tribe,” they wrote. They also argued that approving the pipelines –particularly the DAPL — would undermine treaties the U.S. signed with the Great Sioux Nation in the 19th century.

The Western Democrats also said they believe the U.S. must uphold treaty obligations to the Standing Rock and respect the tribe’s “self-determination,” along with the “wishes of all tribal nations.”

Anti-DAPL activists believe the line’s construction would trample on tribal lands and potentially poison waterways, including rivers such as the Missouri River and Lake Oahe.

Standing Rock Sioux’s tribal council passed a resolution in January calling for camps holding the activists to be dismantled. The resolution did not mention any plans to relocate the 600 activists, most of whom are outsiders.

The tribe has been pushing protesters to vacate the area since U.S. Army Corps of Engineers rejected the $3.8 billion project in December, yet the anti-DAPL activists have refused Standing Rock’s pleas.

Wednesday’s arrests bring the total number of those arrested to 600. State officials continue to ask federal officials for help corralling what they called out of control protesters.

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