The United States is keeping its borders closed for non-essential travel to Canadians for at least another month.

The Department of Homeland Security (DHS) tweeted Friday morning that the U.S. is extending restrictions on non-essential travel at their land and ferry crossing with Canada and Mexico through Sept. 21.

The restrictions were set to expire on Aug. 21.

The decision was made to minimize spread of COVID-19, particularly the highly-contagious Delta variant, amid a fourth wave of the pandemic.

“In coordination with public health and medical experts, DHS continues working closely with its partners across the United States and internationally to determine how to safely and sustainably resume normal travel,” the tweet read.

DHS said essential trade and travel will continue across the border.

Non-essential travel restrictions have been in place since March 21, 2020.

On Aug. 8, Canada opened up its border to non-essential U.S. travellers who are fully vaccinated with Health Canada approved COVID-19 vaccines.