Preventing harmful algal blooms to protect freshwater supplies

When lakes or reservoirs turn bright green, the underlying issue is often a shift in water quality rather than a simple seasonal algae event. Rapid algal growth can affect aquatic ecosystems, recreational use and, critically, the reliability of drinking water sources. In many freshwater systems, blooms are linked to nutrient enrichment combined with warm, stable water conditions.

Cyanobacteria, commonly known as blue-green algae, are a key concern because some species produce toxins, cause taste and odour problems and disrupt treatment operations. For utilities and environmental managers, early detection and mitigation are essential to prevent contamination from reaching water treatment facilities.

Objectives: Reduce contamination risk and protect water resources
The primary objective is to prevent nutrient-driven blooms and minimise their impacts on ecosystems and drinking water operations. This includes limiting nutrient inputs, identifying bloom conditions early, and maintaining stable oxygen levels and ecological balance in surface waters.

How algal blooms contribute to water contamination
Algae are a natural part of aquatic ecosystems, but excessive nutrient loading—particularly phosphorus and nitrogen—can trigger rapid growth. Thick blooms reduce light penetration, smother aquatic vegetation and degrade habitats. When blooms collapse, bacterial decomposition consumes dissolved oxygen, potentially causing fish kills and creating low-oxygen zones that further destabilise the system.

Common nutrient sources include agricultural runoff, leaking septic systems and wastewater overflows. Without intervention, these drivers can cause recurring blooms, especially during warm, calm periods.

Identifying toxic and non-toxic blooms
Visual cues such as green surface scums or odours can indicate a bloom, but toxicity cannot be determined by sight alone. Toxicity depends on the cyanobacteria species present and whether toxins are being produced. Therefore, monitoring programs combine field observations with sensor-based measurements (such as chlorophyll and phycocyanin) and laboratory analysis to assess risk.

For drinking water operators, early identification allows adjustments in treatment processes and supports public health advisories when cyanotoxins are detected.

Role of dissolved oxygen and dead zones
Dissolved oxygen is a critical indicator of water quality. Blooms can increase oxygen near the surface during daylight, but oxygen levels often drop sharply when algae decay. In stratified lakes, oxygen depletion can occur in deeper layers, creating “dead zones” where many organisms cannot survive. These conditions stress ecosystems and complicate water treatment operations.

Impacts beyond toxins
Even when toxins are not confirmed, blooms can still cause surface scums, unpleasant odours, pH fluctuations and repeated low-oxygen events. These effects reduce biodiversity, disrupt nutrient cycles and pose risks to human and animal health through direct contact with contaminated water.

Water management strategies to control blooms
Preventive, catchment-based measures are the most effective long-term approach. Key actions include reducing nutrient inputs, strengthening natural buffers such as wetlands and vegetated shorelines, and establishing early-warning monitoring routines. Progress is typically measured through trends such as fewer high-risk bloom days, lower biomass peaks and more stable raw water conditions.

Preventive technologies and monitoring
In systems with recurring blooms, low-power ultrasound can be used to disrupt algae buoyancy and reduce surface accumulation. Integrated monitoring platforms combine sensors, control technologies and data analytics to provide early warnings and long-term performance insights. Tracking pigments, dissolved oxygen and temperature profiles enables proactive management before blooms impact water treatment or public use.

Conclusion
Preventing harmful algal blooms requires addressing nutrient loading, thermal conditions and water column mixing. Catchment interventions, continuous monitoring and preventive technologies form a comprehensive strategy to protect freshwater ecosystems and drinking water sources. By combining upstream nutrient management with early-warning systems, water authorities can reduce contamination risks, stabilise treatment operations and support long-term freshwater resilience.

www.lgsonic.com