Which pollutant is primarily responsible for causing algae blooms?

The primary pollutant responsible for causing algae blooms is nitrogen. Nitrogen, along with phosphorus, serves as a nutrient that can fuel the rapid growth of algae in aquatic environments. When these nutrients enter water bodies from sources such as agricultural runoff, wastewater discharges, or atmospheric deposition, they can lead to eutrophication—a process characterized by excessive nutrient enrichment. This can result in dense algal populations, commonly referred to as algae blooms.

Algae blooms are problematic because they can deplete oxygen in the water, block sunlight from reaching aquatic plants, and produce toxins that can harm aquatic life and pose health risks to humans and animals. While other pollutants such as pesticides, oils and greases, and heavy metals can also impact aquatic ecosystems, nitrogen specifically plays a critical role in promoting the conditions necessary for algae blooms to occur.