The Earth Day event on the United States' Pacific island territory also served as an opportunity to protest against President Donald Trump's position on climate change.
One of the organisers of the Guam march, the wildlife biologist, Isha Alexander, said Mr Trump is defunding the scientists who demonstrate the climate is changing.
"There are enough statistics out there about green energies and the jobs they create, just like you can create some jobs with oil," Ms Alexander said.
