Mercury and plastic from rivers and lakes can not only harm local ecosystems but also pose a danger to humans, as river water is actively used by humans. And when it reaches the sea, the carcinogen can accumulate in seafood and be ingested by humans. In Greenland, in just the last couple of years, thousands of large blue lakes have turned brown; they’ve filled with stinking mud that releases carbon into the atmosphere. Another study found that mercury levels have nearly doubled in virtually all the world’s major rivers. And the first data collected on plastic pollution in the Amazon basin in 2025 reveals its widespread prevalence.