The four men who recorded themselves illegally walking on the Grand Prismatic Spring in Yellowstone National Park are in more hot water than the thermals they messed with two months ago, according to the latest development in the case.

"The individuals will need to come in person to resolve this matter ultimately," Assistant U.S. Attorney Lee Pico said of them in federal court in Mammoth Hot Springs on Thursday.

That means they almost certainly will be arrested when they enter the United States, not only for what happened at Yellowstone, but for similar cases pending against them at Death Valley and Mesa Verde national parks, Pico said during a telephone status conference with their Laramie attorney Thomas Fleener before U.S. Magistrate Judge Mark Carman.

The U.S. Bureau of Land Management in Utah also has pending charges against them, he said.

According to the minutes of the Thursday's status conference, Pico did not give details about the other pending charges.

Yellowstone's case is now well-known.

On May 14, British Columbia residents Charles Ryker Gamble, Alexey Andriyovych Lyakh and Justis Cooper Price-Brown, and New Zealand national Hamish McNab Campbell Cross recorded themselves leaving the boardwalk at the Grand Prismatic Spring in May, walking across the sensitive bacterial mat covering the area, and reaching into the water.

A park visitor recorded the event and turned it over to authorities. The four were charged with violating a regulation that requires people to stay on designated board walks or trails, and with creating or maintaining “a hazardous or physically offensive condition."

If convicted, they each face up to six months in jail and a $5,000 fine. Because the charges are misdemeanors, the United States would not seek extradition.

They posted their Yellowstone video on their High on Life SundayFundayz Facebook page and website. (They later posted an apology.) Their social media sites also showed them behaving unethically if not illegally at other places including the Bonneville Salt Flats and the Berlin Holocaust Memorial. Their behavior has drawn international outrage on their own and other media sites. A California man even started his own Stop High on Life page on Facebook.

Campbell, Lyakh and Price-Brown returned to Canada. Cross, who was with the three as an independent filmmaker, returned to New Zealand, Fleener said during the status conference Thursday.

Assistant U.S. Attorney Pico said he the research on the cases is done, and he is working with the other national parks to resolve all the cases as one, but that may not be possible. The BLM also is working on the cases, Pico said.

Yellowstone National Park is expecting some restitution for the four men's actions, but he wasn't sure what the other national parks may want.

Because of the National Park Service and BLM cases, Fleener said the three Canadians could have a problem dealing with them because they would be arrested when they try to travel to the United States.

At the end of the telephone status conference, Judge Carman said the court needs to resolve the issue because of the intense publicity about the case. Carman also would like all the cases resolved in Yellowstone because the attorneys involved are from Wyoming.

The next status conference is set for Aug. 8.