A "Dead Zone" refers to an area in a body of water where oxygen levels are so low that marine life cannot survive. These zones often occur in coastal regions due to nutrient pollution from sources like agricultural runoff and sewage. The excess nutrients lead to algal blooms, which deplete oxygen when they decompose, creating conditions unsuitable for fish and other aquatic organisms. The phenomenon is not limited to oceans; it can also occur in lakes and rivers. Scientists monitor these areas to understand their impact on ecosystems and to develop strategies for reducing nutrient pollution, thereby protecting marine biodiversity and fisheries.