Summers bring us joy and a yearning for a soothing dip in our favorite lakes and ponds. Yet, lurking beneath the sparkling surface is a little-known threat to our water quality – Cyanobacteria, or blue-green algae.

Understanding Cyanobacteria

These microscopic organisms exist naturally in both fresh and salt waters. They’re similar to plants in their ability to produce their own food. Cyanobacteria use the energy of sunlight to drive photosynthesis, a process where the energy of light is used to split water molecules into oxygen, protons, and electrons. Though most are harmless, some species generate toxins hazardous to humans and animals.

Cyanobacteria harvest the sun’s energy, absorb carbon dioxide, and emit oxygen. Like plants and algae, cyanobacteria contain chlorophyll and convert carbon dioxide to sugar through carbon fixation., Source: All About Photosynthetic Organisms

When does Cyanobacteria Bloom? Certain conditions prompt cyanobacteria to multiply rapidly, forming large, visible blooms:

  • Heatwaves leading to warmer water temperatures
  • Stagnant or slow-flowing water
  • High levels of nutrients, often from sewage, agricultural runoff, or fertilizers.

The dense accumulation of cyanobacteria cells can create a vibrant, almost fluorescent green color in the water, resembling a paint spill. Think of a lime green paint spill, floating flecks, or algae mats – that’s cyanobacteria bloom.

Cyanobacteria bloom in a steady water body

Overgrown and accumulated toxic cyanobacteria form flakes or clusters of colonies that are scattered in the water column or accumulated on the water surface in the form of a covering or visible mush, the so-called ‘water bloom’, which is most often green and blue-green in colour. The water bloom can move around the reservoir according to the wind direction and get trapped on the banks, where it dries and sprays,” pointed out Zuzana Valovičová from the Department of Environmental Hygiene of the ÚVZ of the Slovak Republic. (4)

The Health Impact of Cyanobacteria

Contact with these toxins, either through inhalation, skin contact, or accidental ingestion, can lead to:

  • Irritation of skin, eyes, nose, and throat
  • Stomach pain, vomiting, and diarrhea
  • Fever, headaches, and muscle weakness
  • In rare instances, severe conditions like liver or kidney damage, or paralysis.

Children and pets are at higher risk due to their likelihood of swallowing water during play. (3)

However, the presence of cyanobacteria doesn’t mean you can’t enjoy a refreshing swim. Even if a bloom is present, there are precautions you can take to minimize risk. By following these simple steps, you can secure a safe water experience (5):

  • Look out for warning signs or advisories
  • Avoid areas with visible algal blooms
  • Do not swallow water while swimming
  • Rinse off with fresh water post-swim
  • Keep pets away from potential bloom areas

Understanding cyanobacteria’s risks and taking necessary precautions will ensure your summer remains enjoyable.

Cyanobacteria Prevention and Management

The primary strategy to control cyanobacterial bloom is reducing nutrient inputs into water bodies. Proper sewage treatment, responsible use of fertilizers, and maintaining vegetation along water bodies can help. Periodic monitoring and emergency planning are crucial for managing these blooms.

Cyanobacteria bloom forming in still water bodies during the summer, Midjourney

Could IoT sensors help?

IoT devices can play a key role in this by providing real-time monitoring and data collection. Sensors placed in lakes and rivers can continuously measure parameters like nutrient levels, water temperature, and dissolved oxygen, alerting authorities to potential bloom-forming conditions. This data can then inform targeted nutrient reduction efforts, such as adjusting fertilizer application or identifying malfunctioning septic systems.

As MERATCH’s Water Expert and Chief Innovation Officer, Andrej Mošať , remarked:

IoT-enabled early warning systems can detect the onset of a bloom and quickly notify the public, allowing them to avoid contact with the contaminated water. Automated water quality monitoring stations can also track the progression and movement of the bloom, guiding emergency response and mitigation strategies.

Periodic monitoring and emergency planning are crucial for managing these blooms. IoT networks integrating water sensors, weather stations, and predictive models can provide the comprehensive, real-time data needed for proactive bloom prevention and rapid response. By leveraging the power of connected technologies, communities can be better equipped to detect, manage, and ultimately prevent the harmful impacts of cyanobacterial outbreaks.


  1. Visual: Each Cell Is A Tiny Ethanol Factory
  2. All About Photosynthetic Organisms
  3. Recreational water and health: Cyanobacteria and their toxins
  4. Zdravé leto 2023: Čo by ste mali vedieť o kvalite vody na kúpanie a o bezpečnom kúpaní sa
  5. Zdravé leto 2023: Čo by ste mali vedieť o kvalite vody na kúpanie a o bezpečnom kúpaní sa