Events included an Earth Day fair in St. John's, NL, a tree planting day in Windsor, Ont. and a parade in Vancouver.
In Montreal, tens of thousands of people marched through the streets to mark the occasion. The march was so massive that, more than two hours after it began, a large crowd was still waiting at the starting point.
Many said they were angered by the Harper government's environmental policies, including its decision to withdraw Canada from Kyoto. Others said they were critical of Quebec Premier Jean Charest's plan to develop the province's north.
"It feels like we're not on the same page," said Melanie Demers, 38, who brought her family to the march.
"It feels as if they're running a business, but I think that it's more than running a business to run a country or a province."
NDP Leader Tom Mulcair, who joined the march, criticized the Harper government for failing to take environmental issues seriously.
He signed a symbolic petition supporting the Kyoto Protocol and lamented what he called the "environmental debt" being racked up at the expense of future generations.
Liberal Environment critic Kirsty Duncan issued a statement slamming the government for its "reckless cuts to climate science, environmental protection, monitoring and industry oversight."
Natural Resources Minister Joe Oliver defended his government's record Sunday, saying the move last week to streamline environmental assessment rules for big projects would be more efficient and create jobs.
"This is a balanced program that will actually strengthen environmental protection, at the same time as bringing the regulatory system to the needs of the 21st century," Oliver said on CTV's Question Period.
"At the same time, we have to make sure that the immense opportunity for economic growth is realized, and we don't get bogged down in duplication."
Many at the Montreal march, though, complained economic growth was valued over environmental and social causes.
The red square that has become a symbol of the student movement against tuition hikes was everywhere, but there were also plenty of young children and babies in strollers.
A sign that read "love the Earth and all students" seemed to sum up the mood, which was far more festive than the recent clashes in Montreal between police and protesters.
Many complained that Charest's policies, on everything from shale gas exploration to nuclear power, don't reflect the values of Quebecers.
Jacqueline Bui, a 36-year-old Montrealer, said Charest's policies serve a "minority of the people while the rest aren't benefiting."
"It doesn't make sense."
Earth Day was launched in the U.S. on April 22, 1970 to raise awareness about environmental issues.
More than six million Canadians take part every year in events and projects to improve their local environments, according to organizers of Earth Day events in Canada.
In order to accommodate all the events, organizers say Earth Day has been transformed into Earth Week and Earth Month. Many communities held events last week while others are planning events this week.
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