A recent study published in the journal Nature shows that as temperatures rise around the globe, the amount of oxygen that is dissolved in the water is decreasing. The rate of decrease is much larger in freshwater lakes than in the ocean. This is concerning because as oxygen levels decrease, life in the streams and lakes becomes much more difficult, and may result in the eventual reduction of fresh-water fish and endangered species. The stream chemistry is also being affected by runoff of agricultural chemicals from farm fields and livestock pens. You can read more about how much the oxygen is being reduced and what it means at https://news.yahoo.com/study-lake-fish-risk-climate-024412006.html.