What primarily causes algal blooms in aquatic environments?

Algal blooms in aquatic environments are primarily caused by an abundance of nutrients, particularly nitrogen and phosphorus. These nutrients often enter water bodies from agricultural runoff, wastewater discharge, and other human activities. When the concentration of these nutrients becomes excessively high, they provide a readily available food source for algae, allowing them to reproduce rapidly and form blooms.

While excessive sunlight, pesticide runoff, and high water temperatures can contribute to the conditions that favor algae growth, they do not initiate algal blooms to the same extent as nutrient enrichment. Sunlight is necessary for photosynthesis, but in many cases, the availability of nutrients is the limiting factor for algal growth. Therefore, without an excess of nutrients, algal blooms are unlikely to occur even if sunlight and warm temperatures are present.