(Photo : Getty Images) Change in Oxygen Levels Scientists examined samples and measurements collected from 393 lakes in temperate regions of the globe across a period from 1941 to 2017, discovering a general decrease in dissolved oxygen in both shallow and deep water habitats. That change in oxygen levels has a contagion effect, all the way from the water biogeochemistry to the health of human populations who may depend on these lakes. It could also bring about boosted greenhouse gas emissions from aquatic bacteria that generate methane. Kevin Rose, an environmental biologist from the Rensselaer Polytechnic Institute said: "All complex life relies on oxygen, It's the aquatic food web's support system. And when you begin to lose oxygen, you have the possibility of losing species."