How to prevent algal blooms in lakes

How to prevent algal blooms in lakes and reservoirs

How can we prevent algal blooms? A question that is often raised. Algae are present in all water bodies naturally. They are an important part of any lake ecosystem.

The level of algae concentration affects the ecological balance. Extensive algal blooms in lakes and reservoirs disrupts the natural balance diminishing the quality of water. If any algal type starts growing rapidly, it can suffocate other creatures living in the water.

The water turns green, tastes moldy, and can be dangerous to drink. Eventually, this can trigger freshwater deficiency, massive death of fish and other aquatic inhabitants.

Restoring a healthy ecosystem balance requires effective control of algae growth.

This article provides a comprehensive overview of the main challenges and benefits of algae control methods.

Jump to

  1. What causes algal blooms?
  2. How to prevent algal blooms?
  3. The dangers of algal blooms
  4. Solutions for algae blooms

Algal bloom causes

What causes algal blooms?

Stagnant water, high temperature, and excessive nutrients stimulate blue-green algae growth. In summer, when the water warms up, algae can grow really fast. Water reservoirs often lack circulation, so the water is stagnant. Abundant nutrients like Nitrogen and Phosphorus help algae over-compete other water organisms creating massive algae blooms.

Algal growth occurs in three major forms (from left to right):

  • Planktonic – single-celled, microscopic algae. They can float in the water freely or form colonies. They can change water color to green, yellow, brown or red.
  • Filamentous algae – single-celled algae forming long hair like mats.
  • Macrophytes – resemble real plants appearing to have stems and leaves.

Algal types

Preventing contamination of water with new nutrients doesn’t really resolve this issue. Growth, decay, gravity, and eutrophication will continue the internal Phosphorus cycle in ponds and lakes.  Human activities like agriculture accelerate eutrophication. This, in turn, provokes the additional release of nutrients stored in the bottom sediments. It can lead to irreversible long-term changes in the ecosystem.

Water quality monitoring system

How to prevent algal blooms?

Algae control helps prevent these environmental, health and safety impacts. Sustainable algae management aims to reduce the inflow of nutrients into the water body. Long-term success requires extensive changes in policies and human activities. So it can take many years to improve water quality significantly.

Real-time monitoring of key water quality parameters and algae indicators helps prevent and predict the risk of algae growth. Monitoring phytoplankton dynamics like Chlorophyll-a, phycocyanin, Temperature, DO, pH, and Turbidity allow forecasting harmful algal blooms. The assessment is based on data about the concentration of algal biomass in a water body.

Bloom assessment and prediction help select effective preventive methods. Treatment methods for algae control include aeration, chemical/biological additives, or ultrasound technology.

The dangers of algal blooms

Excessive cyanobacteria (blue-green algae) and green algae growth in lakes, ponds, and reservoirs can deteriorate their water quality. It releases toxins that often lead to the death of fish and domestic animals.

People can suffer illnesses, paralysis and potentially liver cancer associated with algae contamination. If such water is used for drinking, it can endanger the entire water supply. These toxins and metabolites can dissolve in water escaping the conventional treatment. Their persistence can lead to health concerns, water taste, and odor problems.

Algae dangers

Solutions for algae blooms

Controlling the spread of Cyanobacteria has become a severe global challenge. Especially, for lakes and bigger ponds. Current algal bloom treatment methods all have significant pros and cons. Some control methods are not environmentally safe, for example, Algaecides. Other methods like Aeration, are quite expensive.

To prevent harmful algal blooms, current algae control options that are commonly used include:

  • Ultrasound
  • Chemicals
  • Aeration
  • Mixing

Ultrasonic algae control system

Ultrasonic algae control

Ultrasounds are sound waves with frequencies above the limit of human hearing (22 kHz). At specific frequencies, ultrasound can control algae growth (video). Cyanobacteria use gas vesicles for buoyancy and depth regulation. During the day, algae are photosynthesizing in the top layer. Carbon dioxide and nutrients dissolved in water help them produce oxygen and polysaccharides. At night, the cyanobacteria cells empty their vacuole to sink to the bottom. There, they use oxygen and nutrients to produce biomass.

Ultrasound waves create a sound layer in the top layer of the water. This affects algae buoyancy. The algae cells start sinking to the bottom. There, they cannot photosynthesize without enough light and eventually die. Specific frequency programs must be used to ensure efficiency. Selection is based on the type of algae that requires control. Algae can adapt during seasons within the same lake. The ultrasonic frequencies must be regularly adjusted for successful long-term algal control.

Controlling algae with ultrasound is a well-established technology used for many years. It is proven effective for green and blue-green algae. Ultrasound is environmentally friendly and harmless to fish or plants. It can be used for small and large lakes. Ultrasound integrated with real-time water quality monitoring allows to predict algal blooms and prevent algal blooms.

Must cover the entire surface of the lake. Each spatial spot must be treated for a minimum duration to achieve full efficiency.

Chemical control

Chemical control

Involves treating the water with various chemical additives. Alum, lanthanum, or any other products that precipitate or sequester the ionized orthophosphates. Aquatic herbicides used to treat algae are called algaecides. They are often copper-based compounds (e.g. copper sulfate, copper chelate communes, chemical Endothall).

Effective if the entire surface is treated.

Algaecides are expensive and need frequent dosing. They must be used with care, as they can cause algal cell rupture. This triggers the release of toxins into the water. Rapid decay of harmful algal blooms can contaminate water with high concentrations of algal toxins. This is dangerous for fish and plants. Algaecides can have significant long-term effects on the lake’s ecological balance. They are not suitable for large water surfaces

Lake aeration


Healthy levels of dissolved oxygen in the pond are crucial. Oxygen helps break down the decaying vegetation and other nutrients in the water. Microorganisms help break down the silt at the bottom. Aerobic and anaerobic bacteria both contribute to decomposition.

Aerobic decomposition requires a continuous supply of oxygen. It intensifies when dissolved oxygen concentrations approach the saturation levels. The primary result of aerobic bacteria decomposition is carbon dioxide. Anaerobic decomposition is slower. The end products are organic compounds like alcohols and foul-smelling organic acids.

Aeration is an environmentally friendly technique to rejuvenate water bodies.  It increases the level of oxygen in the water. Aeration systems can help avoid chemical use and create a healthy ecosystem. It can be used for large ponds.

High costs for maintenance and labor, intense energy use. Aeration does not kill the algae directly, so it is not always efficient. It requires treatment of the entire water surface.

Mixing system


Mixing circulates water to achieve destratification in reservoirs. The process involves mixing water to eliminate stratified layers. Epilimnion and Metalimnion are usually circulated to control algae. The aim is to clear the surface water from iron, manganese, and anoxic odors that usually occur in the Hypolimnion layer. This makes conditions less favorable for algae growth in certain layers.

Artificial circulation causes less environmental damage than using chemicals. It is generally more effective in deep reservoirs (mean depth >15 m).

Circulating water requires high systems’ maintenance due to wear and tear. Such systems have fluctuating results on algae blooms. The effect on total cyanobacteria levels is controversial. In lakes, mixing often affects only surface layers close to destratifiers. In large systems, mixing sediments can actually increase the available nutrients. This triggers further algae growth in the short term. However, in the long-term, reductions can be achieved.