Eutrophication is driven by an overabundance of nutrients that fuel excessive growth of algae and aquatic plants. The two nutrients most often responsible are nitrogen and phosphorus. They are essential for plant growth, and when they enter water bodies in large quantities—through agricultural runoff, wastewater, and detergents—plants and algae can multiply rapidly. In freshwater systems, phosphorus is frequently the limiting nutrient, so adding it alone can trigger strong blooms, while nitrogen also promotes growth, especially in other parts of the aquatic food web and in combination with phosphorus. The resulting algal blooms block sunlight, and when the algae die, their decomposition by microbes consumes large amounts of dissolved oxygen, leading to hypoxic conditions that stress or kill aquatic life. The other elements listed—sodium and chloride; calcium and magnesium; potassium and iron—are not the primary drivers of eutrophication. They can influence water chemistry or plant metabolism in various ways, but they do not typically fuel the kind of widespread, nutrient-driven algal overgrowth that characterizes eutrophication.