Background: Environmental activism in Indonesia increasingly depends on hashtagged digital discourse, where ecological harm, public accountability, and civic participation are negotiated through activist texts, visual materials, and platform-oriented communication. Objective: This study examines how Indonesian environmental hashtag activism constructs environmental issues as public-good claims, authorizes civic voice, and makes ecological concerns visible within platformed public discourse. Method: This study applies qualitative digital discourse analysis supported by corpus-assisted mapping of 29 publicly verifiable documents, consisting of activist texts, secondary contextual sources, and regulatory documents coded through public-good framing, civic voice, addressivity, and multimodal visibility. Results: Public-good framing shows that energy transition, ecological justice, land protection, waste governance, Indigenous stewardship, and democratic rights are articulated as shared civic concerns rather than isolated environmental topics. Civic voice is distributed across civil-society watchdogs, affected communities, citizen publics, Indigenous or local stewards, youth-oriented actors, and rights-bearing democratic subjects. Platform visibility depends on hashtag aggregation, institutional address, multimodal evidence, and circulation cues that make environmental claims searchable, attributable, and publicly recognizable. Implication: This study demonstrates that hashtag activism should be understood not as simple online amplification, but as a discursive process through which ecological harm becomes speakable, legitimate, and collectively actionable. Novelty: This study offers an integrated analytical framework linking public-good framing, civic voice, and platform visibility in Indonesian environmental digital activism