The Farmer’s Guide to Toxic Algae Blooms: Causes, Effects, and Prevention

Clean water is the backbone of every farm, from irrigating crops to providing clean water for your livestock. In recent years, toxic algae blooms have become a growing threat to farming operations across the country. These harmful blooms can contaminate water supplies, damage crops, sicken livestock, and cause serious economic losses.

As farmers, we rely on clean water every single day, whether it’s for irrigating our fields, watering our livestock, or making sure our family has safe water to drink. Over the years, I’ve learned just how quickly toxic algae blooms can threaten not only my farm but the entire community around me. These blooms, often triggered by too many nutrients like nitrogen and phosphorus entering our water, can spread fast and cause real damage. At first glance, they might just look like green scum on a pond, but the toxins they release can contaminate drinking water, harm animals, and disrupt farming operations in ways that hit both the land and the wallet.

In this guide, we’ll explain what causes algae blooms, how they can harm farms, and practical steps farmers can take to prevent them.

What Are Toxic Algae Blooms?

Algae have been part of Earth’s ecosystems for over 3 billion years, playing an important role in producing oxygen and supporting aquatic life. They’re a natural part of the environment, but when conditions are just right (or wrong, depending on how you look at it), high nutrients, hot temperatures, and plenty of sunlight, they can explode into massive blooms. These out-of-control algae create a harmful algae bloom (HAB).

Once a bloom takes off, it spreads across the water like a thick blanket, blocking sunlight from reaching plants and animals below the surface. This throws the whole ecosystem out of balance and can kill off fish, plants, and other organisms that are crucial to healthy waterways.

Toxic blooms are usually fueled by:

• Excess nutrients (nitrogen and phosphorus) from fertilizer runoff, manure, and wastewater

• High temperatures

• Still or slow-moving water

• Intense sunlight

  
  

When algae multiply quickly, they form thick mats on the water’s surface. These mats block sunlight from reaching aquatic plants and deplete oxygen levels as the algae die and decompose, a process called eutrophication. This can create “dead zones” where fish and other aquatic life cannot survive.

Why Farmers Should Be Concerned About Algae Blooms

For farmers, this becomes more than an environmental problem; it becomes a health hazard. Blue-green algae (cyanobacteria), which show up in still waters like ponds and lakes, can be extremely toxic. I’ve seen warnings advising folks not to swim, drink, or even fish from contaminated water. On a farm, that means livestock are at risk, and irrigation water may suddenly be unsafe.

• Livestock health – Animals drinking contaminated water may suffer, become ill or even die.

• Irrigation risks – Using algae-contaminated water can spread toxins to crops.

• Economic impact – Crop loss, livestock loss, and halted operations can cause major financial setbacks.

• Community water supply – Many rural communities rely on local reservoirs for drinking water, which can be impacted by farm runoff.

  
  

How Algae Blooms Start

Algae thrive under the same conditions that stress our water systems: still water, hot weather, and excess nutrients. Cyanobacteria feed off carbon dioxide, sunlight, and calm water. You might notice this on your own farm. They photosynthesize as plants do, but instead of helping the ecosystem, they smother it.

As the bloom grows, the water becomes so cloudy—what scientists call “turbidity”—that sunlight can’t reach the plants living below. When the algae eventually die and sink, they’re broken down by bacteria that use up all the oxygen in the water. This creates “dead zones,” where nothing can survive—fish, plants, and other aquatic life all disappear.

Although the blooms usually die off quickly, the damage they leave behind can take years to repair. I’ve watched ponds go from healthy and clear to murky and lifeless in just one season.

Most farm-related algae blooms are triggered by nutrient runoff:

• Fertilizer runoff from fields after heavy rain or overwatering

• Soil erosion carries nutrient-rich sediment into waterways

• Livestock waste washing into ponds, lakes, or streams

Freshwater blooms often involve cyanobacteria (blue-green algae), which produce toxins harmful to humans and animals. These blooms can range from a small patch to covering miles of water surface.

Preventing Algae Blooms on Farms

The good news is that farmers can take proactive steps to reduce the risk of toxic algae blooms. By managing nutrients and improving water protection practices, you can protect your farm and your community.

1. Manage Fertilizer Use

• Soil Testing – Apply only the nutrients your soil needs.

• Variable Rate Application – Apply fertilizer where it’s needed most.

• Timing – Avoid fertilizing before heavy rains to reduce runoff.

• Slow-Release Fertilizers – Reduce nutrient leaching and runoff over time.

  
  

2. Reduce Runoff and Erosion

• No-Till or Reduced Tillage – Minimize soil disturbance and prevent erosion.

• Cover Crops – Plant rye, clover, oats, or barley in off-seasons to hold soil in place and absorb nutrients.

• Buffer Strips – Plant grasses, shrubs, or trees along field edges to trap nutrients before they reach waterways.

• Contour Farming – Plant along the land’s natural contours to slow water flow.

  
  

3. Improve Water Management

• Efficient Irrigation – Use drip systems or targeted watering to avoid excess runoff.

• Livestock Waste Control – Store manure away from water sources and compost before spreading.

• Rotational Grazing – Reduce concentrated manure deposits near waterways.

  
  

Conservation Practices That Work

Some proven conservation strategies for preventing farm-related algae blooms include:

• Vegetative Buffers – Switchgrass, prairie cordgrass, or other deep-rooted plants stabilize soil and filter runoff.

• Agroforestry – Planting trees along waterways to provide shade, reduce erosion, and absorb nutrients.

• Regenerative Agriculture – Building soil health to naturally retain nutrients and water.

  
  

The Bottom Line for Farmers

Algae blooms may be natural, but the scale we’re seeing today is not. As farmers, we’re deeply connected to the land and water. When a bloom kills a pond or contaminates a water source, we feel it immediately, through livestock health issues, reduced crop yields, and financial losses.

But algae also remind us of something else: balance. A healthy environment supports healthy farms. Without careful nutrient management, clean water, and responsible stewardship, our farms and communities suffer.

Toxic algae blooms are preventable. By managing nutrients wisely, reducing runoff, and protecting water sources, farmers can avoid costly damage to crops, livestock, and the environment.

Healthy water means healthy farms, and taking steps now not only protects your livelihood but also supports your community’s water supply for the future.

Farmbrite is an all-in-one record-keeping, breeding, grazing, health, treatments, and cattle management software. Farmbrite is designed for single or multi-species and diverse farms. With the right cattle software and data collection methods, it’s easy to keep tabs on all of the information you need in one place. We pride ourselves on being the best software for cattle management.

Give us a try today.

National Institute of Environmental Health Sciences. “Algal Blooms.” National Institute of Environmental Health Sciences, 16 Oct. 2023, www.niehs.nih.gov/health/topics/agents/algal-blooms.

CDC. “Summary Report – One Health Harmful Algal Bloom System (OHHABS), United States, 2020.” One Health Harmful Algal Bloom System (OHHABS), 15 May 2024, www.cdc.gov/ohhabs/data/summary-report-united-states-2020.html.

NASA Science Editorial Team. “The Good, the Bad, and the Algae.” NASA Science, NASA, https://science.nasa.gov/science-research/earth-science/26jun_algae/.

Zafar, Salman. “How Algal Blooms Affect the Environment | EcoMENA.” Ecomena, 21 Dec. 2022, www.ecomena.org/how-algal-blooms-affect-the-environment/.