Final answer:
Communities in the Colorado River Watershed were most likely affected by the Gold King Mine spill in Colorado in 2015.
Step-by-step explanation:
The communities most likely affected by the Gold King Mine spill in Colorado in 2015 would be those in the Colorado River Watershed. This spill resulted in over 3 million gallons of contaminated water flowing into the Animas River, which is part of the Colorado River Watershed. Such environmental incidents underscore the importance of balancing industrial activities with the protection of our watershed ecosystems, as the consequences of contamination can have far-reaching impacts on human health, local economies, and biodiversity.