We can now view algal blooms from space – it is no secret that they are plaguing our plant.

Harmful algal blooms, commonly referred to as HABs, are congregations of increased algae production that cause detrimental effects to animals, plants, and humans. 2 types of HABs exist: 1) high biomass algal blooms that create oxygen deficient zones as they decompose, and 2) toxic algal blooms that release potent toxins capable of causing illness or even death in aquatic animals and humans, in addition to the oxygen depletion they create upon decay. Expansive oxygen depletion often leads to mass mortality of fish, shellfish, marine mammals, turtles, and aquatic invertebrates.

Human exposure to algal toxins occurs through airborne compounds, swimming in affected waterbodies, and ingestion through food and drinking water. Possible symptoms include but are not limited to: respiratory discomfort, skin irritation, gastrointestinal upset, vomiting, diarrhea, seizers, liver damage, paralysis, and in some cases, death. Consuming toxin-contaminated seafood is particularly dangerous because many algal toxins can bioaccumulate, therefore leading to elevated health risks upon ingestion.

Although algal blooms are naturally occurring, human-induced nutrient enrichment of aquatic ecosystems has intensified the occurrence and severity of harmful algal blooms. Since algae colonize both freshwater and marine systems, no waterbody is immune to their potential destruction. Human alterations of the phosphorus and nitrogen cycles have surpassed safe thresholds and, as a result, eutrophication is predicted to increase in surface water and coastal zones worldwide by 2030 (UNESCO). Agricultural runoff, insufficient wastewater treatment, soil erosion, and pollution are the most commonly discussed causes of algal blooms, but another prominent threat lingers – climate change. Elevated water temperatures promote excessive algal growth and, therefore, further amplify the frequency of harmful algal blooms. Due to the many compounding factors that lead to HABs, experts often rely on interdisciplinary collaborations to offset the ensuing widespread consequences.

Among the most notorious consequences of HABs are the economic ramifications, which are substantial and cringe-worthy. The European Commission identifies commercial fishery impacts, negative tourism influences, human health complications, and monitoring/management costs as the primary economic impacts of HABs. However, a comprehensive list of HAB repercussions is exhaustive: aquaculture stock mortality, aquaculture products rendered inedible due to toxin bioaccumulation, fishing closures, reduced consumer demand for seafood, decreased tourism traffic, impaired real-estate prices, increased medical expenses, inflation of drinking water prices and sanitation costs, desalination infrastructure disruption, unanticipated environmental clean-up costs… and the list goes on.

To put the magnitude of economic impacts into perspective, a highly-cited 2009 study estimated that the economic losses from human-induced freshwater eutrophication in the United  States alone total over $2.2 billion USD annually. Specifically, annual losses were observed to be around $1 billion USD related recreational water usage, $0.3-$2.8 billion USD in waterfront property values, $44 million USD for biodiversity loss prevention, and $813 million USD for drinking water costs. While these numbers are certainly shocking, it is safe to assume that they will rise in the future due to increased HAB occurrence and severity. 

The environmental and societal consequences of harmful algal blooms should also not be taken lightly. Aside from the highly publicized mass fish kills (such as Florida’s current 1-year-long bloom), HABs also alter water chemistry, force fish and marine mammal migration, reduce sunlight penetration for aquatic plants, and ultimately lead to environmental degradation. Algal toxins can bioaccumulate in food webs and, thus, present a serious threat to communities that rely on shellfish and fish for subsistence or income generation. Simply put, blooms can imperil aquatic ecosystems and can threaten food security in many developing nations.

The economic, environmental, and human health risks associated with harmful algal bloom are substantial and minimizing these risks is paramount. HAB forecasting models are being developed by governments, private sectors, researchers, and health authorities worldwide to mitigate the negative effects of incoming blooms.  Scientists combine satellite data with on-the-ground measurements (or perhaps more appropriately coined, in-the-water measurements) to predict the onset, location, and transportation of HABs. Landsat and Sentinel satellites, operated by NASA/United States Geologic Survey and the European Space Agency respectively, offer open-access, up-to-date archives that are commonly employed by forecasters. Satellite imagery and measurements of water color, temperature, wind, and water currents are incorporated into many models. While seasonal and short-term (3-7 day) forecasts are now available online for various regions around the globe, the adoption of HAB forecasting is projected to increase as scientists aim to improve the accuracy, coverage, and duration of predictions.

The United States’ National Oceanic and Atmospheric Administration (NOAA) is one of the many governmental organizations successfully using HAB forecasting to reduce human exposure to algal bloom toxins. Researchers combine satellite imagery, weather forecast information, and water current models to produce up-to-date reports of existing HABs and offer bloom forecasts for western Lake Erie and the Gulf of Mexico. This information is utilized by public water system operators, public health authorities, tourists, anglers, and beach-goers to minimize health risks and maximize safety. Actions may include preparing water treatment plants for microcystin (cyanobacteria toxins) removal, releasing public health advisories, implementing beach closures, and avoiding algal infected areas for recreational purposes (swimming, fishing, etc.).

Until recently, aquaculture producers in Ireland often found themselves at the whim of HABs. Repercussions included mass mortality of fish, commercial fishery closures for extended periods of time, and shellfish stocks had been rendered inedible from toxin bioaccumulation, but algal bloom forecasting is helping to change that narrative. The Marine Institute in Ireland has successfully developed a HAB forecasting model and releases weekly algal bulletins that inform the aquaculture industry and regulators of potential bloom risks.  The bulletins include an accurate 3-day forecast, phytoplankton distribution maps, descriptions of current trends and summaries of historical trends. Early warnings help to reduce the negative economic consequences of algal blooms by giving aquaculture producers enough time to implement appropriate precautionary measures. This could include optimizing yield schedules to avoid toxin bioaccumulation by early or delayed harvest, installing aeration systems to combat oxygen depletion, and/or moving their stocks elsewhere.

Harmful algal blooms are a highly personal environmental issue; they affect people’s livelihoods, drinking water, food, and health. Although strategies such as minimizing consumption, implementing public health advisories, restricting access to algal infected areas, and altering aquaculture practices can effectively manage the risks associated with blooms, we must collectively invest greater effort into eradicating HABs altogether. A significant reduction of nutrient leaching into water bodies is needed to secure the future health of our aquatic ecosystems and protect the people who rely on these precious resources. Targeted and decisive governmental policy is necessary to create widespread societal action, but the power we hold as citizens must also be harnessed. Making environmentally responsible choices, such as reducing lawn fertilizer applications, purchasing low nitrogen and phosphorus products, as well as maintaining efficient septic systems, and supporting clean-water legislation are easy yet significant ways to reduce our individual eutrophication burdens.

Algal blooms are a stark reminder of our impacts on aquatic ecosystems. They stain our rivers, lakes, and oceans, and leave destruction in their wake. I suggest that we each take a pause to reflect on our contribution to global eutrophication and begin to change our relationship with water. Whether you are a government official with policy-making influence, a scientist researching these blooms, or a citizen choosing to reduce your environmental footprint, we all have a part to play in the fight against harmful algal blooms.


Cox, Christopher. “Toxic algal bloom continues to suffocate Florida’s Gulf Coast.” United Nations Environment Online. Last modified September 6, 2018. https://www.unenvironment.org/news-and-stories/story/toxic-algal-bloom-continues-suffocate-floridas-gulf-coast

Dodds, Walter K., Wes W. Bouska, Jeffrey L. Eitzmann, Tyler J. Pilger, Kristen L. Pitts, Alyssa J. Riley, Joshua T. Schloesser, and Darren J. Thornbrugh. "Eutrophication of US freshwaters: analysis of potential economic damages." Environmental Technology & Science 43, no. 1 (2008): 12-19.

 “Experimental Lake Erie Harmful Algal Bloom (HAB) Tracker.” National Oceanic and Atmospheric Administration – Great Lakes Environmental Research Laboratory. Accessed October 25, 2018. https://www.glerl.noaa.gov/res/HABs_and_Hypoxia/habTracker.html.

“Gulf of Mexico Harmful Algal Bloom Forecast.” National Oceanic and Atmospheric Administration – Tides and Currents. Accessed October 25, 2018. https://tidesandcurrents.noaa.gov/hab/gomx.html.

“Landsat.” NASA. Accessed October 25, 2018. https://www.nasa.gov/mission_pages/landsat/main/index.html.

Sanseverino, Isabella, Diana Conduto, Luca Pozzoli, Srdan Dobricic, and Teresa Lettieri. Algal bloom and its economic impactReport no. EUR 27905, European Union. 2016.

 “Sentinel Online.” European Space Agency. Accessed October 25, 2018. https://sentinel.esa.int/web/sentinel/home.

“Weekly HAB Bulletin.” Marine Institute. Accessed October 25, 2018. http://www.marine.ie/Home/site-area/data-services/interactive-maps/weekly-hab-bulletin.

WWAP (United Nations World Water Assessment Programme). The United Nations World Water Development Report 2015: Water for a Sustainable World. Paris, UNESCO. 2015.