What Are the Causes of Harmful Algal Blooms?

Harmful algal blooms, or HABs, are the increased presence of certain species of algae within a lake, river, ocean or other water system. These HABs occur both in freshwater and saltwater environments, and are deemed harmful due to the damage they cause to the environment. This damage is caused when the excess algae consume the majority of the oxygen in the water, causing other marine life to die in mass numbers. The HABs can also contaminate shellfish and seafood, leading to possible severe food poisoning and death.

Increased Amount of Nutrients in Water

• If a naturally occurring increase of nutrients appears within the water system, algal blooms are common. These situations arise when there is less marine life consuming nutrients in a water system and where there is an abundance of aquatic plant life releasing nutrients into the water.

Abundance of Oxygen in Water

• An abundance of oxygen within the water system significantly increases the amount of algae that form. Because these individual organisms operate at the microscopic level, they quickly respond to an increase in oxygen by reproducing. Within a few days, the levels of algal blooms caused by an abundance of oxygen rise greatly.

Warmer Water Temperatures

• When the temperature of water rises, even by a few degrees, tremendous changes begin happening in the marine environment. For algal blooms, warmer water means an increased amount of oxygen and nutrients being dissolved in the water. This spawns additional reproduction by the algae and quickly escalates into a significant problem.

Human Impact

• Human pollution plays a major role in the formation of HABs. The waste dumped into water systems is often rich in the type of nutrients that feed algae. If a strong enough concentration develops, the algal blooms begin immediately and continue to expand as long as the flow of nutrients continues to enter the water system.