Teacher leaders, despite their significant contributions to schools, are often undervalued and underutilized. Even with increased interest in the literature over the past few decades, there remains a lack of empirical studies, especially on informal teacher leaders who remain full-time classroom teachers while taking on extra duties. In light of the current global situation, one informal teacher leader role is emerging as especially vital -- environmental teacher leaders who are responsible for fostering whole-school sustainability initiatives. The aim of this qualitative study was to investigate the factors that help or hinder EcoSchool teacher leaders in Ontario, Canada when taking on a school-wide leadership role. Findings showed that these teacher leaders faced numerous barriers, including challenges that are unique to the role of an environmental leader. Results highlighted the key role of the principal in helping teacher leaders overcome resistant school cultures and inhibitive school structures. These findings bring to light the challenges environmental teacher leaders face and emphasize the essential role principals need to play by distributing their leadership to better support teachers as school leaders.