Forecasting, Prioritizing Hypoxia & HABs Risks and Remediating Them

By Frank Slovenec Co-Executive Director, Global Water Works

Frank Slovenec

2022 was a significant year for the recognition of HABs and the directive to develop processes that will predict and remediate them. In June 2022, the U.S. Government Accounting Office produced the GAO Report on Harmful Algal Blooms (HABs). The GAO has raised the alarm! It says it is time to set a national goal and establish a national program to predict, prevent and remediate the toxic Harmful Algae Blooms.


Phosphorus and Nitrogen are depicted as the enemy, but they are not toxins, they are nutrients. Nutrients produce biomass. The problem with eutrophic water bodies is that there is too much invasive weed, algae and cyanobacteria biomass produced and not enough animal biomass in the food web to consume and clear nutrient-rich biomass.

Nutrients are valuable, and managing eutrophication should be focused on directing nutrients into the production of the right biomass for a healthy, balanced ecosystem that supports natural nutrient processing. Using consumers of algae and bacteria to control eutrophication is a valid approach, but in practice can run into many issues. For examples, cyanobacteria and other species are not nutritive/edible enough to support consumers, they grow too fast for consumers to keep up, and eutrophication leads to fish kills that cause imbalances throughout the food web–all undermining top-down management.

It’s generally more effective to control blooms by controlling nutrient inputs. However, the chronic deterioration of our lakes and failure to manage the risks of hypoxia and HABs reflects the extent to which existing metrics miss the mark for assessing nutrient loads and the inappropriateness of the measures taken to address them, i.e. the bottom-up approach to management.

Conventional analysis is too often a study in complication and confusion. (Cyanobacteria in reservoirs, causes, consequences, controls). Misguided symptomatic metrics inevitably lead to misguided symptomatic responses. As the GAO report points out, these symptomatic treatments are not merely ineffective, but exacerbate the problem.

The GAO is succinct and insightful in its analysis, focusing on:

  • Hypoxia,
  • Organic sediment build-up, driving hypoxia and nutrient recycling
  • A shift to a predominance of undesirable species (HABs) as the relevant factors and metrics.

Each of these metrics is indicative of the degree of progression of the eutrophic process towards the inevitable onset of HABs. Therefore, an objective way to quantify these metrics must be the basis for such a methodology. These parameters are not currently a focus in conventional lake status assessments.

Modern sonar bathymetry is a fundamental assessment tool used in successful prevention and remediation projects that has not been used by regulatory agencies to date. Bathymetric scanning allows the development of two key metrics after measurement of the depth at which dissolved oxygen levels are low enough to be hypoxic:

  • The volume of water that is hypoxic and thus denied to animal life responsible for nutrient clearance
  • The surface area of sediment that is hypoxic and therefore sustaining feedback loops of oxygen depletion and nutrient recycling.

These two measures provide an effective, relevant way to monitor and compare the risk profile of a lake. Fortunately, with modern technology, lake residents can take their own DO readings so that scores for these two metrics can be calculated and tracked over time.

The third key parameter is the extent to which “undesirable species” – cyanobacteria – have managed to exert their dominance. This metric can be determined by taxonomic analysis of water samples taken from a lake by local authorities or citizen scientists.


Residents trained on sampling processes not only accelerate monitoring efforts, but they can speed awareness, prevention, and remediation programs.

By incorporating these three metrics into a scorecard, lake users have a simple, cost-effective way to measure and share the status of lakes and forecast their likely trajectory.

GWW is engaging a leading national academic institution and technology companies in developing this scorecard to help prioritize eutrophic lakes for treatment.

We know measurement is the key to management, and our hope is the scorecard will provide a mechanism to assess the general health of our lakes. And, where hypoxia or harmful algae are detected, we can implement multi-level methods for efficient nutrient cycling.*


After decades of watching the problem get worse and relying on reactive mitigation and control responses after the fact, the Government Accountability Office says it is time to set a national goal and establish a national program to prevent toxic Harmful Algae Blooms.

This 8-minute video summary of the GAO Report provides a high-level overview:

GAO Report Conclusions:

The GAO identifies four key shortcomings in managing Hypoxia and HABs to date:

1. Reliance on reactive responses after HABs comprising:

  • “mitigation” or warnings and publicity about the HAB event
  • “controls” such as algaecides which kill algae cells that sink into the sediment and worsen hypoxia (paying to make the problem worse)

2. Lack of a program to collect relevant data to inform the prioritization of preventative actions
3. Lack of a national goal for Hypoxia and HAB prevention
4. Lack of understanding of the costs of current reactive responses (mitigation and control) versus the benefits of prevention.

Clear Recommendations

The GAO calls for:

1. A national goal to prevent hypoxia and HABs in freshwater sources
2. A national Hypoxia and HABs prevention program
3. Performance measurement of the national Hypoxia and HABs prevention program
4. Monitoring, forecasting and prioritizing of water bodies for preventive interventions.
5. Better information and guidance to state, local and tribal governments on the cost/benefits of prevention over mitigation and control.


GAO Report Online

GWW 10-minute Guide

*Prevent and Remediate HABs Group

Expert Panel Responds to GAO Report at the Michigan Inland Lakes Conference

All are invited to participate in the Global Water Works community. GWW is a non-profit community of 2,600+ members over 100 countries and all 50 states, open to all seeking solutions to water issues. We connect People, Processes and Technologies to solve water issues locally to scale globally.

Global Water Works’ Mission: To solve the Global Water Crisis in this generation.
Focus Areas

We have three key focus areas that we are prioritizing on our global agenda this year:

1. Restoring Lakes
2. Harvesting Rainwater
3. Point of use water, Sanitation and Hygiene in emergency situations and for the poor.

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Opinions expressed here do not necessarily reflect those of the Sustainable Phosphorus Alliance.