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What causes an algal bloom in a lake or ocean?

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“mermaid's wine glass” algae — Algae The macroscopic genus of algae known as *Acetabularia* is commonly called “mermaid's wine glass” because of the distinctive umbrella-like shape of the tips of its stalks.

An algal bloom occurs when a population of microscopic photosynthetic organisms, such as algae, diatoms, or dinoflagellates, experiences rapid and dense growth in a body of water.12

These blooms are primarily caused by an abundance of nutrients—specifically nitrates and phosphates—coupled with adequate sunlight. While some blooms occur naturally due to seasonal shifts or upwelling that brings nutrients to the surface, many are triggered or accelerated by human activity, a process known as cultural eutrophication.13

Key drivers of these nutrient-rich conditions include:
* Agricultural Runoff: Fertilizers from croplands wash into waterways, providing a massive influx of nutrients.452
* Domestic Sewage: Human waste and detergents contribute significant levels of nitrogen and phosphorus to aquatic systems.43
* Industrial Waste: Runoff from industrial sites can further increase nutrient loads.1

When these nutrients fuel excessive growth, the resulting bloom can deplete oxygen levels, block sunlight, and release toxins, which may harm aquatic life and threaten human health.132