Data Deep Dive: Understanding Hypoxia in Lake Erie

May 27, 2024

Lake Erie is a tremendous source of fresh water, home to diverse aquatic life, and an economic and innovation hub for many industries. But with climate change and human activities affecting the environment, impacting soil, air, and water quality, and environmental shifts, including the decline of ice coverage across the Great Lakes, changes continually occur in Lake Erie. Even natural and seasonal variations in water quality, including temperature, pH, and oxygen levels, can cause an imbalance in the vibrancy of ecosystems and aquatic life and significantly impact public health and safety.

Data monitoring and the ability to collect, analyze, and compile information are essential in understanding and safeguarding one of the world’s largest freshwater sources.

As part of our ongoing mission to impact the Great Lakes region and freshwater systems worldwide, Cleveland Water Alliance's Smart Lake Erie Watershed Initiative supports a telecommunications network of over 200 sensors and 20 smart buoys, spanning a growing 6,500 square miles of the Lake Erie watershed and collecting a variety of data.

Our very own CWA data expert, Dr. Jeff Pu, has been reviewing, analyzing, and forecasting trends from the data. We are happy to share those insights and information in our Data Deep Dive blog series.

In our last Data Deep Dive, we reviewed a severe storm event that swept across Lake Erie from August 29th to August 30th, 2023, and discussed the importance and implications of such information. In our exploration, we found how invaluable Lake Erie data is and how essential data sharing with our partners is to champion our water resources. Many entities, organizations, and individuals, rely on our real-time weather and maritime information to operate their business and recreational activities, including utilities and water treatment facilities, those responsible for maintaining our potable water supplies and water systems.

The ability to monitor water conditions at drinking water intakes is critical to the water treatment process. Our buoys can observe a range of conditions across Lake Erie including wave heights, wind speeds, water temperature as well as the amount of oxygen in the water. Real-time data from buoys near water intakes provides critical data directly to water plant operators.


In this Data Deep Dive, we discuss hypoxia, a decrease or depletion in oxygen levels that naturally impacts Lake Erie throughout the year. In our quest to analyze the collected data, we sat down with Freeboard Technologies’ Ed Verhamme and Aqua Ohio’s Bill Bowers and George Ginnis.


Oxygen is a necessity for our entire planet, an invaluable resource for human beings, animal life, and plant life alike, and the need for oxygen in water is no different. The decrease in oxygen levels in water can have a devastating impact on aquatic ecosystems. 


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Hypoxia can disrupt ecosystems, marine biodiversity, and have significant recreational and economic impacts on fisheries as well as water treatment. There are a variety of causes of hypoxia but in Lake Erie, it most often occurs in mid to late summer through the biological decomposition of organic matter in the bottom layer of the lake near the sediments. Dead algae and river runoff sink the bottom of the lake and take years to decades to fully decompose. In the summer, the bottom layer of the lake is thermally isolated from surface waters and oxygen can’t be replenished by exchange with the atmosphere. The bottom layer of cold hypoxic water also contains many dissolved minerals and a lower pH, which can further complicate the water treatment process. Though the hypoxic layer stays near the bottom of the lake, it can move due to winds and water currents that push this hypoxic layer closer to shore and towards the shoreline and water intakes.

"If this hypoxic, dead water comes up to shore, the fish can't go anywhere, so they get trapped in it and they can die in large masses," explained Ed Verhamme, President of Freeboard Technologies (the Ohio subsidiary of LimnoTech).

The lack of oxygen makes it nearly impossible for small fish and other life in water to survive, but the rippling impacts do not stop there. An overabundance of dead fish impacts the marine food chain, and too many decaying fish can overwhelm natural decomposers that help break down carcasses, which keep marine ecosystems balanced. This excessive amount of decomposed fish releases gases and chemicals into the water, which can substantially change the composition, impacting the overall quality of the water.

Often, the naturally decomposing matter stirred up in the hypoxic waters from the bottom of the lake has a sulfur-like odor that coastal communities can smell when the dead zones move near shore. Sometimes this can be confused with a gas leak, as natural gas pipelines are mixed with sulphur gas to ensure you can smell a leak.


An event captured by our sensor network demonstrates the significant consequences of a rapid change in Lake Erie's conditions, specifically a shift in the amount of dissolved oxygen in the water. On August 7th, 2023, our smart buoys detected an sharp decrease in dissolved oxygen at the Ashtabula water intake; oxygen saturation levels dropped from 100% to approximately 54%, an astonishing forty-six percent decrease in one day. Following the event, oxygen content returned to its normal range of 90% saturated. We also noted a coinciding change in turbidity at this time, which indicates strong winds were mixing the nearshore waters.

Turbidity measures the cloudiness of water caused by particles. The data shows the turbidity level detected by our sensors increased from 0 to 1000 NTU (nepheloid turbidity units), indicating an increase in potential sediment, particles, and other organic/inorganic material in the water in conjunction with the hypoxic event.

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With shifts in water clarity, the overall quality of the water changes, creating a different atmosphere for aquatic life. In further analysis of our smart buoy data, we discovered another interesting event that highlighted the need for constant water monitoring to maintain an up-to-date understanding of the health of Lake Erie; In August 2023, we noted a potential upwelling incident from Sunday, August 27th to Tuesday, August 29th. 

Our nearshore buoys measured a decrease of dissolved oxygen (from 6mg/L to hypoxic levels (< 2 mg/L)) on Tuesday, August 29th, which was consistent with a previous National Oceanic and Atmospheric Administration (NOAA) forecast.

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Our Cleveland offshore buoys continued capturing data suggesting hypoxic conditions persisted since mid-July 2023.


The health of our water supplies and public health are intricately linked. Long-term shifts in oxygen levels and the clarity of the water could potentially lead to a mass die-off of marine organisms. Pathogens and other hazardous microorganisms entering our water can have devastating and lasting effects on our communities and the animal and plant life we share the planet with, reaffirming the need to monitor Lake Erie to mitigate harmful affects of poor water quality. Water treatment facilities and utilities that use the abundant freshwater resource provided by Lake Erie are keenly watching the lake's pH, turbidity, temperature, and dissolved oxygen levels as they treat the water for distribution to the community. Advanced technology can now autonomously monitor conditions on the lake, which supplement manual measures of the same parameters in the plant.

To understand the impact of both these hypoxic events and their impact on drinking water treatment, we spoke with our partners at Aqua Ohio. Aqua Ohio is the one of the largest drinking water and wastewater utility in Ohio, serving about 500,000 residents across 19 counties. The company has been proactive in upgrading its infrastructure, with significant investments into technological advancements including software and predictive modeling tools that will help them treat incoming water with more efficiency and effectiveness. Our conversation gave us expert insight into the water management and treatment processes and highlighted how crucial real-time water monitoring data is as they treat the water for public consumption.

Aqua Ohio partnered with CWA in 2023 to relocate some near-shore buoys closer to their Lake Erie water intakes in both the Ashtabula and Mentor areas. This allows them to have more accurate data on lake conditions before they reach their treatment facilities, especially near the bottom of the lake.

On a day-to-day basis, water treatment facilities that use Lake Erie as a source for drinking water are analyzing data about the quality of the incoming water. Our partners at Aqua Ohio have observed an industry-wide shift toward software tools and predictive data models that help them get insights into what may be ahead, rather than merely reacting to what is coming in. 

“We’re seeing the water quality conditions come in across the lake, in real-time, and it's a nice early warning system for the people at my level," explained George Ginnis, Production Manager for Aqua Ohio’s Ashtabula treatment facility.

George stated that they regularly use NOAA’s Hypoxia Early Warning Predictive Data to understand when conditions indicate a possible hypoxic event. However, they now can confirm the predictive data in real-time with information accessible from CWA’s Smart Buoys.

"I'll be able to see low pH and low dissolved oxygen, and that's an early warning indicator for us to know that the conditions are actually occurring so that we can tweak our treatment process slightly to be more prepared for a hypoxic event as it comes in." 



The technological advancements needed to capture this type of information were not always readily accessible or available. Earlier technology did not allow for real-time, cost-efficient data collection of environmental conditions. Hypoxic events were predicted by watching the skies, paying attention, and reviewing weather conditions. 

Water taken in during hypoxic events undergoes a different treated differently than water under normal lake conditions. This allows Aqua Ohio to be more proactive, efficient, and effective in their treatment, ensuring that the water going into our communities always remains safe and pure.

Bill Bowers, Area Manager of Aqua Ohio, shared, "It does change our treatment process when we experience hypoxic water. It changes our chemical strategy which results in more cost spent on chemicals.” The ability to predict hypoxic events ahead of time provides cost savings for utilities and water treatment plants, as varying conditions like hypoxia require a different standard of chemicals and treatment protocols.

Along with forecasting, cost-savings, planning, and preparedness for adjustments in treatment processes, buoy data empowers employers with the tools they need to train new team members. It gives new employees access to data on historical trends and insights to help them understand weather and environmental conditions and recognize patterns that may lead to hypoxic events.

"When you give people new employees tools like the buoy, you can show them 'oh, look at what the lake did yesterday and see that was weird,' ... you could talk to them about the thermal structure of the lake. You can show them how that correlated with the weather,” Verhamme points out, in contrast to the intuitive training it has taken in years past, to understand these weather patterns and their impacts on water treatment processes.

In the last 15 years, data collected from the National Oceanic and Atmospheric Administration (NOAA) has also provided essential information and historical trends on water and weather conditions. And, with the additional data captured from the smart buoys, utilities like Aqua Ohio have an incredible addition to their treatment toolkit.

"Prior to the buoy, the main tool for being aware of hypoxic conditions was those NOAA forecasts. So now, in conjunction with the buoy data, we have a lot more tools at our disposal to deal with that type of water if we see it,” Bill Bowers noted.

With recent advancements like CWA’s smart buoys and NOAA data now available, planning for events and other conditions that impact water systems can be forecasted through predictive modeling, which helps to inform water management and treatment decision-making processes. With predictive modeling and event forecasting, treatment facilities can be more proactive and adjust their treatment protocols to manage potential water challenges like hypoxic events.


It is abundantly clear that monitoring and collecting data on Lake Erie is invaluable. Hypoxia is a reoccurring event that happens annually, and with data collection and tracking becoming more proficient, experts have seen large fluctuations in the size of hypoxic events in the last five years. Though hypoxic events are a natural part of lake condition, the size and duration of the events can be linked to human activity on land including agricultural runoff and from public sewage treatment plants. To help maintain our waterways, we must continue to track and collect information on the lake, gathering intelligence on weather, environmental conditions, and adverse events that can impact marine life and our communities, which heavily rely upon water resources.

The network and infrastructure deployed by Cleveland Water Alliance continue to play a vital role in delivering real-time monitoring and data collection, providing historical and current information about water conditions and other environmental parameters. The data from the lake provides significant information and insights into our freshwater source.

Lake Erie, a warm body of water and home to half the population of fish inhabiting the Great Lakes, is an incredibly invaluable resource; through partnership and collaboration, we can continue to ensure the lake thrives for generations to come.

As Bowers enthusiastically remarked, “It's important to remember that hypoxic events aren't something that happen every day and we are prepared when it does, but most of the time, Lake Erie an amazing source of water to treat from. Hypoxic events probably happen 2% of the time. So 98% of the time, the lake is a fantastic source of water, and we're lucky and blessed to have that resource here.”


Recommended reading: The Chicago Tribune wrote an entire series on hypoxia, hypoxic events, and other Lake Erie conditions and challenges. For an even deeper dive into hypoxia, check out the series here

Lake Erie's Dead Zone: PDF

USGS: Turbidity and Water

USGS: Dissolved Oxygen and Water

Hypoxia, “aquatic hypoxia,” or oxygen depletion is often a naturally occurring event. In bodies of water, oxygen depletion causes “dead zones”  where marine life can’t survive. It is typically characterized by oxygen levels below 2 mg/L.

“Turbidity is a measure of the level of particles, such as sediment, plankton, or organic by-products, in a body of water. As the turbidity of water increases, it becomes denser and less clear due to a higher concentration of these light-blocking particles.” Learn more: Source

Upwelling is a natural phenomenon that brings nutrient-rich water from the bottom of the lake to the surface.

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