Toxic Algae

Although most blooms of green algae are not harmful, there are some that have the ability to produce toxins – called harmful algae blooms (HABs) or toxic algae.  Remember, you can still boat, fish and recreate in Kentucky’s rivers, lakes, and streams.  Just be aware that HABs exist.  …and WHEN IN DOUBT, STAY OUT!

KWA hopes that this is a comprehensive review of toxic algae in Kentucky that will provide you with the information you need to safely enjoy Kentucky’s waterways.  If there are other concerns or questions, please contact us so that we can better inform the citizens of Kentucky.

What is toxic algae?

Algae are photosynthetic organisms that are natural and vital components of healthy ecosystems.  However, when conditions are favorable, algae can rapidly multiply into blooms.  Some of these algae blooms produce dangerous toxins, but even non-toxic blooms hurt the environment (fish kills) and local economies (decrease in recreational use).

Harmful algae blooms are also known as HABs, toxic algae, blue-green algae, cyanobacteria, or under extreme conditions can cause Dead Zones. Toxic algae are found worldwide, and there are at least 46 different species that have been found to have toxic effects in vertebrates.

These toxic algae strands can pose a threat to humans and animals when consumed in water or by contact during recreational activities.  Their levels of toxicity can be diverse, from rapid onset of rashes, headaches, nausea, diarrhea, vomiting, abdominal pain and cramping, to seizures,  liver damage, and possible carcinogenesis from prolonged exposure.  Severity of the illness is related to the amount of water ingested and the concentration of the toxin.

Current research is exposing another real danger of HABs, and potentially more threatening than the toxins, are the other pathogenic microbes that seem to thrive in association with the blooms.  See more here

What are the causes?

These algae blooms need:

      • Sunlight (these are photosynthetic organisms)
      • Warm weather
      • Slow-moving, or low turbulence, water (so they aren’t dispersed)
      • High levels of nutrients, nitrogen and phosphorus (food for the algae), that enter the water from the air, surface water, or groundwater
        • Agriculture: Animal manure, excess fertilizer applied to crops and fields and soil erosion (solutions)
        • Stormwater: Precipitation falls on our cities and towns, runs across hard surfaces, and carries pollutants into our waterways. (solutions)
        • Wastewater: Sewer and septic systems do not always operate properly or remove enough nutrients before discharging into waterways. (solutions)
        • Fossil Fuels: Electric power generation, industry, transportation and agriculture all increase the amount of nitrogen in the air through their emissions. (solutions)
        • In and Around the Home: Fertilizers, yard and pet waste, certain soaps and detergents, landscape choices, and amount of hard surfaces. (solutions)

In Kentucky, these conditions are most often found in our lakes, reservoirs, and ponds during the summer months.

What are the effects?


Human populations who are susceptible include infants, elderly, pregnant women, and anyone who is immuno-compromised.  Pets and wildlife can also be at risk of adverse health risks.

      • Direct exposure from drinking, accidentally swallowing or swimming in contaminated water can cause serious health problems including:
        • rashes
        • stomach or liver illness
        • respiratory problems
        • neurological affects
      • Byproducts of water treatment
        • Stormwater runoff carries nutrients directly into rivers, lakes and reservoirs which serve as sources of drinking water for many people. When disinfectants used to treat drinking water react with toxic algae, harmful chemicals called dioxins can be created. These byproducts have been linked to reproductive and developmental health risks and even cancer.

Economic and cultural implications:

Can raise treatment costs for drinking water. Also, hurts industries that depend on clean water.  This includes recreation on our area rivers, lakes, and streams and can also include industrial processes that intake water from these sources. Coastal HAB events have been estimated to result in economic impacts in the United States of at least $82 million each year. These impacts stress the importance of understanding HABs and developing tools to mitigate their impacts and ultimately to control or even prevent them (source).

Where is it in Kentucky?

Army Corps of Engineers Lake Conditions – updated areas of concern.

The Kentucky Division of Water Hazardous Algal Blooms page has information from across the state.

How do I know if the water is safe?

Unfortunately, this is a hard question to answer and that is part of what makes this threat so scary.  As recreational users of our waterways we are expected to make educated decisions about our level of contact with that water. The only way to know for sure whether toxic algae is present is to examine a water sample under a compound microscope to identify the type of algae.  If you have the technical tools and expertise the Field Guide to Algae and other “scums” in ponds, lakes, streams and rivers, or this Graphic Rendering of Microscopic Appearance are valuable tools. If  you are like most citizens, your safety is based upon your own educated decision.  The following guidelines should help you make that decision:

      • Signs that toxic algae might be present in the water:
        • Warnings issued by the USACE based on World Health Organization Guidelines for Safe Practices (Table 8.3, page 150).  (It is also interesting to compare other state’s advisory policies forHABs.)
          • HAB “advisory”
            • >20,000 cells/mL of cyanobacteria cell counts = contact discouraged, water may be unsafe
          • HAB “caution”
            • > 100,000 cells/mL of cyanobacteria cell counts = closure, contact prohibited
        • Bad odors coming from the water
        • Discolored water or scum on the surface of the water
      • Precautionary measures include:  
        • Avoid stagnant water, particularly when the wind has been blowing in the direction of that stagnant water (see image).  
        • Avoiding contact (especially with sensitive areas such as the ears, eyes, mouth and throat) with visible algae and don’t swallow water.  
        • Taking a bath or shower with warm, soapy water after coming in contact with water in ponds and lakes, especially before preparing or consuming food.  
        • Pets and livestock should also not be allowed to swim in or drink untreated water from these sources. Livestock, pets and wild animals can be poisoned by the toxins produced by some algal blooms. Small animals can ingest a toxic dose quickly.  
        • Dogs are particularly susceptible to blue-green algae poisoning because the scum can attach to their coats and be swallowed during self-cleaning.  
        • Remove fish skin and organs before cooking, do not consume or allow pets/animals to consume the organs or skin.


What can you do?

RM_Toxic Algae Infographic FINPreventative measures are the preferred approach to managing the occurance of HABs. The most effective preventative management practices seek to reduce the nutrient loads from both point and nonpoint sources.

What if you see a HAB?

  • Stay out of the water that may have a HAB.
  • Do not let your children or pets play in HAB debris on the shore.
  • After contact with lake water, even where no HABs are visible, rinse off with fresh water as soon as possible.
  • Never swallow any lake or river water.
  • Do not let pets lick HAB material from their fur or eat HAB material.
  • Do not drink or cook with lake water.
  • See a doctor if you or your children might be ill from HAB toxins.  If your pet appears ill, contact your veterinarian.
  • If you plan to eat fish that you catch, remove the guts and liver, and rinse the fillets in tap water before eating.
  • Report the bloom to the Louisville District Water Quality Team by email at or call (502) 315-7439.

What are government agencies doing about this emerging HAB problem?

In 1998, Congress passed the Harmful Algal Bloom and Hypoxia Research and Control Act (HABHRCA) to address HABs that impacted living marine resources, fish and shellfish harvests and recreational and service industries along the U.S. coastal waters. In 2004, Congress reauthorized and expanded HABHRCA by passing the Harmful Algal Bloom and Hypoxia Amendments Act required federal agencies to assess HABs to include freshwater and estuarine environments and develop reports and plans to reduce the likelihood of HAB formation and to mitigate their damage.  On February 12, 2014, HABHRCA passed the U.S. Senate and passed to the U.S. House of Representatives for consideration.

Currently there are no U.S. federal guidelines, water quality criteria and standards, or regulations concerning the management of harmful algal blooms in drinking water under the Safe Drinking Water Act (SDWA) or in ambient waters under the Clean Water Act (CWA). However, several countries outside the U.S. do have various values that serve as guidelines or thresholds for certain management actions. (source)

Nationally, EPA scientists are working collaboratively with the Army Corps of Engineers (USACE) to understand the drivers of algal bloom dynamics, using statistical modeling to test for significant spatial and temporal trends.  The data set is being provided by the USACE and includes phytoplankton taxonomy, water chemistry, and hydrology measures from 20 reservoirs in Ohio, Kentucky, and Indiana.  The monitoring program has been in place since 1978 and includes multiple sampling sites and depths within each reservoir.  The data set will be used to test multiple hypotheses regarding the drivers of harmful algal blooms in reservoirs. 

Locally,  U.S. Geological Survey, the Corps of Engineers, the Kentucky Division of Water, Kentucky Department of Fish and Wildlife, the Kentucky Department for Public Health and the Kentucky Department of Parks are working together to:

    • Continue water quality monitoring and provide results to the public
    • Monitor any potential blooms on site at the lake
    • Post advisories at the lake in conspicuous places – either “advisory” (potential health affects) or “caution” (more significant risk of health impacts of HAB)
    • Keep boaters, swimmers and those who recreate at the lake informed of the possible risks

With more than 300 lakes in Kentucky, frequent sampling for what amounts to a newly identified health threat is impractical. If you have good predicting tools, you don’t have to collect as much data taken from C-J blog



World Health OrganizationEPAField guide to algae and other “scums” in ponds, lakes, streams and riversKY Dept of Environmental Protection: DOW: HABsMRSA From lakeGreat Lakes Green Algae Protects Harmful BacteriaTrent Roberts Honors Capstone Paper

Is this the same thing as the Dead Zone in the Gulf of Mexico?

Not really.  The algae bloom in the Gulf of Mexico is on a much larger scale, but this type of algae doesn’t always release toxins.  Instead, it chokes out the ecosystem by using up all of the available oxygen as it decays!

Notice how the Gulf of Mexico Dead Zone always occurs around the same time of year as other algae blooms – in the summer?  That is because the naturally occurring algae have a perfect environment to proliferate.

Sunlight and warm weather: The temperature begins to rise as all of the excess northern runoff from spring rains and snow-melt drains down the Mississippi River.

Nutrients: The Mississippi River Basin accounts for over 1,245,000 square miles (41% of the US) in 31 states and contains 52% of American farms.  This entire area flows into the Gulf of Mexico where algae eats the abundance of waste (nutrients) and proliferates.  The algae grows, dies, and then sinks to the bottom where it is decomposed by bacteria that use up all of the available dissolved oxygen.  Animals that can not move away from the area of low oxygen die, creating a Dead Zone.

Here is a brief flash animation to explain the process.

Low turbulence: Without all of the spring storms, the water doesn’t get churned up, keeping the ocean floor so low in dissolved oxygen that it can no longer support living aquatic organisms.