Harmful Algal Blooms
What are the health and environmental impacts of harmful algal blooms?
Research Highlights:
- Harmful Algal Blooms (HAB) are large growths of algae and other microorganisms that release toxic compounds.
- These blooms hurt ecosystems, make humans and animals sick, and have negative effects on fisheries and the tourism industry.
- There are federal and state monitoring programs to help track HAB appearances and growth.
Harmful algal blooms (HAB) are expansive growths of algae and other microorganisms. Freshwater HABs are predominantly cyanobacteria (also known as blue-green algae), which cause large green mats of growth (NOAA n.d.). Saltwater HABs are predominantly phytoplankton and can look green, brown, or red (NOAA n.d.).
There are three requirements for cyanobacterial growth (USDA):
- Warm, slow-moving water (fresh or salt water)
- Sunlight
- Nutrients (primarily nitrogen and phosphorus)
Cyanobacteria and phytoplankton are not harmful unless they start to “bloom,” or grow uncontrollably. Blooming results in toxin and harmful gas release into the environment (CDC, 2022).
There are major HABs seen in Lake Erie (freshwater HAB) every summer for the last 20 years and in the Gulf of Mexico (saltwater HAB) every summer for the last 40 years. However, less frequent occurrences of algal blooms started long before in both areas (Ai et al. 2023; Pennock et al. 2004).
The increased occurrences of HABs are caused by the interplay of several factors (Smith, King, and Williams 2015; Gobler 2020; Wells et al. 2020; Heil and Muni-Morgan 2021):
- Runoff of fertilizer and manure into waterways provides the necessary nutrients for these blooms to occur.
- Increased temperatures in oceans and lakes, due to climate change, allows for longer blooming seasons.
- Pollution and invasive species weaken the local ecosystem and provide opportunities for algal growth.
Certain farming practices, like excess fertilizing, applying manure and fertilizer in the winter, tile drainage, and no-till farming, have exacerbated annual algal blooms (Smith, King, and Williams 2015). Another major contributor to nutrient runoff is the overfertilization of urban and residential lawns and gardens (Trottet et al. 2022).
HABs have negative impacts on local ecosystems.
HABs destroy local ecosystems and cause illness in humans and animals.
Blooms outcompete native and beneficial aquatic plants for sunlight and nutrients (US EPA 2023). The death of environmentally important plants disrupts the local food chain, harming aquatic animals (National Office for Harmful Algal Blooms 2019). HABs also directly harm fish by clumping up in gills and preventing breathing (National Office for Harmful Algal Blooms 2019).
As the algae die they are decomposed by other marine microorganisms, further depleting oxygen from the water in a process called eutrophication (US EPA 2023). The lack of dissolved oxygen leads to aquatic animal and plant death in the area.
HABs have negative impacts on human health.
Cyanobacteria and algae both contribute to HABs, but cyanobacteria excrete toxins into the air and water, known as cyanotoxins (US EPA 2022). These toxins give off bad smells and cause allergic reactions, dermatitis, gastroenteritis, kidney and liver damage, and seizures (USGS 2019; US EPA 2022; Abdallah et al. 2021).
Most cyanobacterial toxins release when cells die and lyse (burst open), discharging their metabolites and toxins into the environment. However, some cyanobacteria will also excrete toxins while they are living (US EPA 2022).
HABs impair the quality of freshwater reservoirs. In 2014, the reoccurring HAB in Lake Erie resulted in suspended drinking water for 500,000 Toledo residents for three days (Brooks et al. 2016; National Office for Harmful Algal Blooms 2019).
Cyanotoxins also bioaccumulate in fish and other aquatic animals consumed by humans (Abdallah et al. 2021). Therefore, even people who do not swim in contaminated water or drink contaminated water could unknowingly eat contaminated fish and shellfish from HAB-containing waterways.
Illnesses in humans and animals due to toxins from freshwater blooms have been seen in 43 states nationwide (USGS 2019).
HABs have negative impacts on the local economy.
The decrease in tourism due to HABs has likely cost the US billions of dollars; Florida alone has lost nearly $3 billion from HAB-related tourism declines (Alvarez et al. 2023).
HABs cost aquaculture 8 $billion/yr globally due to fish death and contamination (Brown et al. 2020). Smaller, local fisheries are hit the hardest due to necessary increases in regulations around contamination. For example, local California fisheries have struggled in recent years due to contaminated stock (Jardine et al. 2020).
People living nearest HABs bear the brunt of increased regulations’ costs, including additional screening and filtering of HAB-infected freshwater. Toledo, Ohio residents have experienced a nearly $100 increase per year in water bills, for a family of five, to get filtered water from Lake Erie (Freed 2022).
Federal and State Regulation
Harmful Algal Bloom and Hypoxia Research and Control Act was originally enacted in 1988 and has been amended and updated in subsequent years. This act created a federal task force to monitor, predict, and control HAB events, with a focus on the Great Lakes and later on the Gulf of Mexico (US EPA 2021). The main agencies involved are the National Oceanic and Atmospheric Administration (NOAA) and the Environmental Protection Agency (EPA).
Additionally, the EPA created a Total Maximum Daily Load program under the Clean Water Act that aims to reduce nutrient pollution in waterways by setting limits on the amount of pollutants that can be discharged into them (US EPA 2015).
The United States Geological Survey tracks the water quality of the nation’s streams and rivers (USGS 2019). States also have water monitoring systems, and fish and shellfish toxin monitoring systems, to ensure that consumers do not accidentally ingest contaminated fish (NOAA n.d.).
HAB monitoring is particularly important in coastal states and Great Lakes states; each has a monitoring system. Michigan, a key Great Lakes state, uses the Michigan Harmful Algal Bloom Reports map to display its tracking data (MI EGLE n.d.).
To see what your state’s monitoring system is, visit https://www.epa.gov/cyanohabs/state-habs-monitoring-programs-and-resources.
