Final answer:
Working to convince companies to reduce their water use has the greatest positive effect on the environment.
Step-by-step explanation:
The action that would have the greatest positive effect on the environment is working to convince companies to reduce their water use.
Water conservation is crucial for sustaining ecosystems and protecting natural resources.
By reducing water use, companies can help preserve freshwater sources, support biodiversity, and mitigate the impacts of human activities on the environment.
Learn more about Impact of Humans on Ecosystems