Carrying signs that read, “Little minds are listening” and “Don’t have polio? Thank science,” thousands of science fans took to the streets Saturday at Toronto’s March for Science.

Dan Weaver, one of the organizers of the march on a chilly Earth Day, said participants were motivated to “celebrate Canadian science and the role that science plays in our society… and to stand in solidarity with American scientists who are facing obvious struggles with the current government and its support for science.”

Signs that said “Science – It’s inconvenient … Sad,” and “Fossils are for learning not just for burning” were held up as a crowd Toronto police estimated at 3,000 made its way from Nathan Phillips Square to Queen’s Park.

The Toronto march was one of at least 600 planned across 68 countries Saturday to protest the policies of U.S. President Donald Trump and his government.

Weaver noted that Canadians and Americans breathe the same air and, in many cases, drink the same water.

“We have a shared economy and a shared environment,” he said. “Decisions in the U.S. have a huge impact on Canadians. If they lower their environmental standards, we breathe the impact of that decision. It is important that we stand together and face these challenges.”

One of the participants in the march, Anna Kobb, was there with her dog, Apollo, 7. “As an American who did not vote for Donald Trump, I am really concerned about policies he is trying to put in place, especially around the (U.S. Environmental Protection Agency),” she said.

Stacey Shannon, who came to the march with a paper mache image of Trump, said she was there to bring awareness to “facts.”

“I’m not a big fan of this ‘alternative facts’ business,” said Shannon, who works at the Ontario Science Centre.“There are facts, and science can help us establish them.”