Why is the Willow Project facing unprecedented backlash?

On March 13, US President Joe Biden approved the Willow Project, a large-scale oil and gas drilling operation in Alaska. According to a March 14 report by CNN, over one million letters were sent to the Biden administration against the project, and over 5 million signatures were gathered on a Change.org petition to halt Willow. What is the Willow Project, and why is it facing unprecedented backlash?