E-Mail IMAGE: Oxygen levels in the world's temperate freshwater lakes are declining faster than in the oceans. view more Credit: Gretchen Hansen, University of Minnesota TROY, N.Y. -- Oxygen levels in the world's temperate freshwater lakes are declining rapidly -- faster than in the oceans -- a trend driven largely by climate change that threatens freshwater biodiversity and drinking water quality. Research published today in Nature found that oxygen levels in surveyed lakes across the temperate zone have declined 5.5% at the surface and 18.6% in deep waters since 1980. Meanwhile, in a large subset of mostly nutrient-polluted lakes, surface oxygen levels increased as water temperatures crossed a threshold favoring cyanobacteria, which can create toxins when they flourish in the form of harmful algal blooms.