Why can strong upwelling in the Arabian Sea sometimes cause mass fish deaths?

Strong upwelling in the Arabian Sea occurs during the summer when deep, nutrient-rich waters are brought to the surface. While these nutrients support marine life, they can also trigger a water bloom—a dense, rapid growth of microscopic organisms like algae or dinoflagellates.12

Mass fish deaths can occur during these events because the massive population of microorganisms may deplete the water's oxygen content as they respire or decompose. Additionally, some of these organisms release toxic substances that can poison aquatic animals. While upwelling is a natural process essential for replenishing nutrients, the resulting biological blooms can create environmental conditions that are lethal to fish populations.21