A Paradigm Shift In Reservoir Management

By Dave Shackleton

Reservoir managers are utilizing a risk management framework along with innovative metrics to address the root causes of lake degradation, including eutrophication, hypoxia, and harmful algal blooms.

It has been more than 25 years — a quarter of a century — since the U.S. EPA and the National Oceanic and Atmospheric Administration (NOAA) were tasked with managing the escalating risks posed by eutrophication. 

This persistent issue causes hypoxia, devastates aquatic ecosystems, and triggers toxic cyanobacterial blooms. Despite decades of effort and significant investment, the problem worsens each year with no meaningful progress in prevention or reversal.

In response, industry professionals are adopting professional risk management strategies for reservoirs that prioritize safety, sustainability, and efficiency. Aligned with established risk management practices, this approach applies structured methods for identifying, analyzing, and mitigating risks. The reservoir risk scorecard improves transparency and decision-making, supporting long-term water resource sustainability.

The Industry’s Wake-Up Call

In 2020, alarmed by the fact that the prevalence and intensity of hypoxia and HABs continue to grow, Congress and the Senate commissioned the Government Accountability Office (GAO) (for a second time) to investigate this failure. The resulting 2022 GAO report, titled, Water Quality: Agencies Should Take More Actions to Manage Risks from Harmful Algal Blooms and Hypoxia, delivered a stark assessment of existing policies and practices and the threats posed to national water security. 

The GAO report highlights a key flaw: federal efforts focus on reacting to HAB outbreaks rather than addressing the systemic causes of eutrophication and hypoxia. This reactive approach, necessary for short-term crisis responses, has failed to address the systemic drivers of eutrophication and hypoxia. 

The report made two key recommendations: firstly, develop monitoring protocols to assess conditions, forecast risks, and prioritize actions, and secondly shift from reactive HAB control to proactive interventions targeting the root causes of eutrophication and hypoxia.

These findings are significant. While eutrophication and HABs affect residential lakes and the lake lifestyle, the impact on drinking water reservoirs is critical. These reservoirs are essential for public health and national water security, yet they face growing threats from ecological degradation and management inefficiency.

“To meet these challenges, a fundamental shift in reservoir management is required that is rooted in the principles of professional risk management and aligned with the GAO’s recommendations,” says Dave Grote, VP of Engineering & Operations at Clean-Flo International, a leading U.S.-based OEM of biological solutions for managing water quality in environments such as lakes, reservoirs, rivers, and wastewater treatment facilities.

This framework integrates risk identification, analysis, evaluation, and response strategies tailored to the unique challenges of water resource management professionals. 

Risk Identification

Effective risk management begins with identifying the key drivers and threats to reservoir integrity. These risks stem from a complex mix of environmental, human, and historical factors that fuel eutrophication, hypoxia, and HABs.

Climate Change and Extreme Weather

Climate change intensifies reservoir stress with greater volatility and extreme weather events. Droughts lower water levels, concentrating nutrients and expanding hypoxia. Wildfires add nutrient-rich ash, while stormwater and floods deposit excess sediments and nutrients. Heat waves warm surface waters, promoting stratification, hypoxia, and cyanobacteria dominance.

Increased weather volatility destabilizes reservoir ecosystems, pushing them toward tipping points. Cyanobacteria thrive in these conditions, while beneficial organisms require stability, accelerating degradation and highlighting the need for resilience-building solutions.

“We are seeing covert signs of eutrophication in many reservoirs, where stratification and benthic hypoxia are locked in for most of the year. In several cases, spring and winter turnover is not fully mixing the water column, leaving a permanent hypoxic layer at the bottom. This sets the stage for cyanobacteria HABs and contributes to blooms occurring earlier in the year, sometimes even during winter, and lasting into late fall. Effective risk management starts with preventing hypoxia all year round,” says Grote.

Accumulated Historic Nutrient Inputs In Sediments 

Many reservoirs face decades of nutrient loading. Organic sediment stores phosphorus and nitrogen, acting as a high risk "time bomb." Under stratification and oxygen depletion, these nutrients are released, fueling cyanobacteria and triggering HABs. This internal recycling becomes a self-sustaining driver of eutrophication and HABs.

Urban Development

Urbanization increases nutrient runoff into reservoirs as impervious surfaces accelerate stormwater flow, carrying pollutants. Wastewater discharges further add nitrogen and phosphorus, exacerbating eutrophication.

Misguided Historic Management Practices

Ironically, algaecides and herbicides worsen eutrophication. While they kill off blooms, decomposing algae deplete oxygen and release nutrients into sediment, intensifying long-term hypoxia.

Similarly, precipitants deposit phosphorus into sediment, causing nutrient buildup and recycling. These short-term fixes worsen long-term reservoir degradation.

Harmful Algal Blooms (HABs) and Public Health Risks

Harmful Algal Blooms (HABs) threaten public health and drinking water because cyanobacteria release toxins causing gastrointestinal, liver, and neurological issues, while aerosolized cyanotoxins pose risks to nearby residents.

Litigation Risks

Growing awareness of HAB risks increases litigation risks for negligent reservoir management, including cases linked to cyanotoxin exposure. 

Economic damage, higher treatment costs, disrupted water supplies, and falling property values may lead to lawsuits or penalties. Utilities that fail to act risk reputational damage and loss of public trust.

Risk Analysis

The GAO’s findings underscore that existing approaches to managing eutrophication, hypoxia, and harmful algal blooms (HABs) are reactive and inadequate, leaving reservoirs vulnerable to escalating threats. A closer examination of these practices reveals fundamental flaws in currently mandated monitoring, control, and mitigation strategies.

Monitoring

Monitoring is essential but often reactive, identifying cyanotoxins after HABs occur rather than preventing root causes like eutrophication and hypoxia.

Effective management requires tracking oxygen, nutrient recycling, and phytoplankton. With this data predictive tools can give insight on HAB risk and inform preventive strategies. 

Controlling 

Algaecides fail to address HAB root causes and often worsen them. Killing cyanobacteria releases toxins, depletes oxygen, and recycles sediment nutrients, fueling eutrophication and future blooms. They also eliminate beneficial algae, giving cyanobacteria a competitive edge.

Mitigation

Reactive measures like warnings and closures protect public health but highlight risk management failures. Events like Toledo’s 2014 “do not drink” advisory that lasted five days disrupt economies, raise treatment costs, erode trust, and increase legal and reputational risks.

Risk Evaluation

Reservoir risks are dynamic and cumulative, driven by decades of management mistakes, legacy nutrient stockpiles, and climate change. 

Expanding hypoxic zones and nutrient buildup increases the likelihood of tipping points being reached and HABs occurring. Degraded water quality limits recreation, harms local economies, and disrupts drinking water treatment, often requiring costly upgrades. 

Proactive management is essential, not optional.

For objective risk evaluation and management, new metrics are needed to assess, track and compare reservoir risks. In response to the GAO’s call for root-cause-focused methodologies, the Reservoir Risk Assessment and Tracking System (RRATS) was developed. 

RRATS monitors key indicators like dissolved oxygen, cyanobacterial populations, and sediment nutrient stockpiles, providing a data-driven basis for risk assessment and prioritizing preventive interventions and measuring their impact.

The Reservoir Risk Index (RRI) uses RRATS data to generate an objective risk score, offering actionable insights by identifying high-risk reservoirs, forecasting future trends, prioritizing resource allocation, and providing a transparent framework for stakeholder communication.

Proactive Risk Management

The assessment of risks and potential responses highlights the definitive conclusion reached by the GAO: the most effective path forward lies in proactive prevention. 

RRATS and RRI support prevention-focused strategies by assessing and monitoring efforts to reduce hypoxia and HAB risks. Key strategies include increasing oxygen levels, managing nutrients, controlling sediment, and improving biological conditions.

Oxygenation 

Oxygenation is key to eliminating hypoxia and preventing HABs. While various aeration systems exist, costly deployment failures have occurred, but RADOR is the only proven scalable solution for large, deep-water bodies.

Unlike aeration, RADOR maintains uniform oxygen levels throughout the water column, preventing oxygen-depleted layers and suppressing nutrient release from sediments.

Bio-Dredging

Bio-dredging is a natural, cost-effective method to reduce nutrient-rich sediments driving eutrophication. Using biological processes and enzymes, it breaks down organic sediments without the disruption, haulage, and high costs of mechanical dredging.

Biological Augmentation

Biological augmentation introduces micronutrients to boost competition to cyanobacteria to prevent HAB formation and restore the foundation layers of the food web to restore natural nutrient clearance pathways. 

A multi-level risk management program improves raw water quality, reduces chemical treatment costs, and simplifies regulatory compliance by minimizing disinfection by-products (DBPs).

The Path Forward

The risk landscape for reservoirs is increasingly complex, shaped by factors beyond management control such as volatility of weather patterns and the legacy of inadvertent historical mismanagement. The GAO report has emphasized a crucial need for a paradigm shift from reactive, symptom-focused strategies to proactive, preventative approaches that target root causes.

RRATS and RRI represent the first practical steps toward implementing the GAO’s recommendations. By providing a structured, data-driven framework to assess risks, prioritize interventions, and measure outcomes, they enable a proactive shift toward root-cause management and long-term reservoir health.

Dave Shackleton (contact@clean-flo.com) is president of Clean-Flo International.