The "Grace and Frankie" co-stars led the first Fire Drill Friday rally of 2020, which ended with Waterston among a group of demonstrators who were taken into custody after calling out bosses of fossil fuel companies for contributing to the threat of global warming.
Friday's (January 3) incident marked the 79-year-old's second arrest, less than three months after he was busted when he first marched alongside Fonda.
The "Barbarella" icon managed to avoid trouble with police this week, having previously found herself under arrest on five other occasions since launching the protests in early October (2019).
Also taking part in the latest gathering was director Josh Fox and "Big Little Lies" child star Iain Armitage, who had last shown his activism spirit in late November as the 11-year-old pounded the pavement in Washington, D.C. to demand immediate action from lawmakers.
The news emerges a week after Fonda and Waterston's castmate, comedienne Lily Tomlin, was taken into custody in a post-Christmas Fire Drill Friday protest.