A satellite image from South Africa shows a vivid, verdant mass of algae and invasive aquatic plants covering the surface of the Hartbeespoort Dam, a recreational reservoir in South Africa. The phenomenon, known as "hypereutrophication," releases toxic chemicals into the water and leads to "dead zones" that can cause widespread fish fatalities. The reservoir, which was constructed in the 1920s, is fed by the Crocodile River and is used for recreational activities. However, it is also home to invasive species such as water hyacinths and Salvinia minima, which cover the reservoir's surface in large, intertwined mats. The algae within the reservoir can produce toxins that must be filtered out of the water for it to be safe to drink. These algae also consumes oxygen from the water below, leading to a toxic "dead zone" when it spreads widely. The water has been polluted with runoff from runoff courses from farms and golf courses, threatening wildlife and causing rashes on water-sports enthusiasts and sick dogs.