Scientists warn that the world’s rivers are running out of oxygen

Rivers around the world are quietly running out of oxygen — and climate change is emerging as the main culprit. A sweeping global analysis of more than 21,000 river systems found that nearly 80% have been steadily losing dissolved oxygen over the past four decades, threatening fish, biodiversity, and the overall health of freshwater ecosystems. Surprisingly, tropical rivers are being hit the hardest, even more than rivers in rapidly warming polar regions.