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What Causes Algal Blooms?

By Chris Dinesen Rogers
Agriculture is a Major Cause of Algal Blooms

Algal blooms occur when there is explosion of algae growth in an aquatic environment. As algae grows and dies, it fills the water with bacteria. These bacteria increase in numbers, depleting the waters' oxygen resources. The result is that plants and fish die off, sometimes to the point where the waters become biological dead zones and are unable to support life.

Agricultural Runoff

Agricultural runoff introduces fertilizers into water resources, increasing the levels of phosphate, phosphorus and nitrogen, resulting in an increase of algae growth.

Human Activities

An increase in nutrient availability can occur from human activities such as logging, road construction and development, which can deposit high levels of nutrients and organic matter into aquatic ecosystems, causing algal bloom.


Flooding of sewer systems can release high levels of phosphorus into water systems, acting like fertilizers and stimulating algae growth.

Fossil Fuels

Emissions from the burning of fossil fuels introduces nitrogen into aquatic habitats, which, in conjunction with high levels of phosphorus, set the stage for algal blooms.

Eutrophic Lakes

Lakes classified as eutrophic systems naturally have high levels of algae that occasionally will increase due to increased photosynthetic production.


About the Author


Chris Dinesen Rogers has been online marketing for more than eight years. She has grown her own art business through SEO and social media and is a consultant specializing in SEO and website development. Her past work experience includes teaching pre-nursing students beginning biology, human anatomy and physiology. Rogers's more than 10 years in conservation makes her equally at home in the outdoors.