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Severn Sound Environmental Association

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Severn Sound Open Water Monitoring Program  


In the past, Severn Sound experienced excessive phosphorus enrichment. This resulted in excessive algae growth, leading to poor water quality conditions for recreational uses such as swimming, and low oxygen conditions for cold water fish communities. In 1985, Severn Sound was listed as an Area of Concern (AOC), one of the most polluted on the Great Lakes. Led by Environment Canada and the Ministry of the Environment, the communities surrounding Severn Sound developed a Remedial Action Plan (RAP), the goals of which were to improve water quality and restore a healthy ecosystem in Severn Sound.

Implementation of the RAP resulted in reduced phosphorus loads through sewage treatment plant upgrades, agricultural projects, private sewage system upgrades, and stormwater treatment. This in turn led to significant improvement in the water quality of the Sound. In 2003, restoration targets had been met, and Severn Sound was delisted as an AOC. The RAP continued as the Severn Sound Environmental Association (SSEA), which monitors 14 stations throughout the Sound in an effort to detect long-term changes in water quality. SSEA continues to monitor water quality and work with municipal partners to ensure that the quality of Severn Sound is maintained.

Monitoring in the open waters of Severn Sound began in 1973 by the Ontario Ministry of Environment. Five stations were regularly sampled - one in each bay of Severn Sound, and one in the open waters. In 1997, the Severn Sound Environmental Association (formerly the Severn Sound Remedial Action Plan) took over regular monitoring, which continues today.

SSEA’s Open Water Monitoring Program monitors the open waters of Severn Sound for indicators of eutrophication. The Severn Sound RAP Stage 3 Report called for continued monitoring of Severn Sound in order to assess changes in trophic status in relation to remedial actions and other ecosystem changes in the area (e.g. invasive species, water level changes).

Sampling MethodSevern Sound Open Water Sampling Equipment

Fourteen open water stations are sampled every 2 weeks during the ice-free season. Water clarity is measured using a Secchi disk, and measurements of temperature, dissolved oxygen, and conductivity are taken every metre from surface to 1 m off bottom. Water samples are taken throughout the sunlit portion, or euphotic zone, of the water column at each station (2x Secchi disk depth) and are analyzed for basic chemistry, nutrients, including total phosphorus, total ammonia, total nitrate, and total Kjeldahl nitrogen, as well as chlorophyll a and metals. Zooplankton and algae samples are also taken.

   View the SSEA Monitoring Station Map (Open water stations are represented by the black triangle symbol)

 Descriptions of Water Quality Variables

Total Phosphorus

This is a measure of the concentration of organic and inorganic (e.g. bound to sediment) forms of phosphorus in the water. Lakes are considered eutrophic, or enriched, at values over 30 µg/L, and oligotrophic, or unenriched, at values under 10 µg/L. Mesotrophic, or moderately enriched lakes have concentrations between 10-30 µg/L.

Total Ammonia, Total Nitrogen, Total Kjeldahl Nitrogen

These measure various forms of nitrogen. Ammonia and nitrate are highly available to plants and algae, and tend to be used up quickly, leading to a sharp decline in concentration between spring and fall. Total Kjeldahl nitrogen is an organic form of nitrogen.

Chlorophyll ɑ

This is a pigment found in all plants and algae, and the amount in a water sample is related to the amount of algae in the water. Values over 5 µg/L indicate eutrophic conditions, while values under 2 µg/L indicate oligotrophic conditions.

Secchi disk depth

This is a measure of the water clarity, which can be affected by sediment or algae in the water. "Tea" coloured waters (e.g. in Honey Harbour area embayments) can also have low clarity due to the tannic acids leaching from nearby wetlands. The target for Severn Sound is 3 m, and 2 m in Penetang Harbour.


Temperature regulates many chemical and biological processes, from algae production to dissolved oxygen concentration, to timing of fish spawning. It important to measure temperature to give context to water quality results, and to track impacts of climate change.

Dissolved Oxygen

Fish and aquatic insects require adequate levels of dissolved oxygen to survive. Low oxygen levels in bottom waters can be a symptom of eutrophication, and can lead to fish kills. Low oxygen can also be caused by natural processes, such as breakdown of large amounts of organic inputs from upstream wetlands.


This is a measure of the amount of dissolved matter in the water. Generally, waters originating from the Precambrian shield (e.g. Honey Harbour) have low conductivity, while waters originating from limestone based regions (the majority of Severn Sound) have higher conductivity. Extreme values indicate a source of pollution.

Factors Affecting Water Quality

Severn Sound is a dynamic system that is influenced on a regional scale by the entire Great Lakes system (e.g. introduction of invasive species like zebra and quagga mussels (Dreissenids) and spiny water flea (Bythotrephes), climate change, fluctuating water levels), and on a local scale by its surrounding watershed (point and non-point additions of nutrients and other contaminants).

 Trends in Severn Sound Water Quality


These are essential for growth and reproduction of living organisms. Two key nutrients are phosphorus and nitrogen. Although naturally found in the environment, excessive amounts create imbalances in plant and animal communities and can adversely affect our recreational water use. Phosphorus is the most limiting nutrient for algal growth, so increases will lead to increased densities. Phosphorus concentrations have decreased below the target of 15 µg/L for Severn Sound and 20 µg/L for Penetang Harbour, set in the Remedial Action Plan. Reduced phosphorus loads from upgrades to sewage treatment plants, agricultural stewardship projects, private system upgrades and stormwater treatment have played an important role in reducing nuisance algae growths and restoring the water quality of Severn Sound. Nitrogen is also an important nutrient for algal growth. Sources can be both natural (air and soil) and anthropogenic (fertilizers, animal and human waste). Nitrate, the form of nitrogen most available to algae, has been increasing since 1970. However, since phosphorus concentrations have declined, and it is the limiting nutrient, increased levels of nitrate are unlikely to lead to increased algal biomass.

Total Phosphorus Results 1969 to 2014 at Severn Sound Monitoring Stations  Nitrate Results 1969 to 2014 at Severn Sound Monitoring Stations 

Water Clarity

​Measured using a Secchi disk, this is a measure of the amount of particles (sediment and algae) and colour in the water column. Over the last decade, clarity has increased at all stations and target levels of 3 m for Severn Sound and 2 m for Penetang Harbour have been achieved. The large increase in clarity around 1994 coincides with the zebra mussel invasion, as well as several major upgrades to sewage treatment plants that discharge to Severn Sound. A slight decrease in recent years may be related to lower water levels in Georgian Bay-Lake Huron.

Water Clarity Results 1969 to 2014 at Severn Sound Monitoring Stations 

Secchi Disk Measuring Water Clarity in Severn Sound 

Chlorophyll ɑ

​This pigment is found in both plants and algae and is related to the amount of algae in the water column. Over the last decade, chlorophyll concentrations have decreased, reaching target levels of 5 µg/L for Severn Sound and 7 µg/L for Penetang Harbour. This has resulted in increased water clarity, and indicates that fewer algal blooms are occurring.

Chlorophyll ɑ Results in Severn Sound 

Phytoplankton (Algae)

These microscopic plants grow suspended in the water column. Population densities can vary throughout the season depending on light, temperature, and nutrient availability. The right combination of these factors can result in algal blooms, which can affect the taste and odour of drinking water, and cause beach fouling. All stations have shown a decrease in the total biovolume of algae.

INTERESTING LINK: What causes Blue-Green Algal Blooms? MOECC - We asked our scientists series video - May 2017


Phytoplankton Trends in Severn SoundFragilariaVolvoxTabellariaUnderwater view of Mougeotia, a type of Algae  Surface view of Mougeotia, a type of Algae  Close up view of Mougeotia, a type of Algae  Microscopic (100X) view of Mougeotia, a type of Algae 



These microscopic invertebrates live suspended in the water column. Sometimes called the “lawnmowers of the lake”, most feed on algae and other particles found in the water column. They are important food for larval stages of all fish and for adult forage fish. Despite normal annual fluctuations, the number of zooplankton species, or diversity, has increased, which is a healthy sign. However, overall densities have declined in recent years, for reasons that are unclear at this time, and may be related to regional stressors. Zooplankton help keep algal populations in check through their grazing activities.

Zooplankton Trends in Severn Sound Ceriodaphnia lacustris Cyclopoida Bosmina longirostrisDaphnia galeata mandotae 

 Daphnia Video

Importance of Long Term Monitoring

It is important to measure a wide range of variables that describe various parts of the aquatic ecosystem in Severn Sound from physical characteristics like temperature, to chemical constituents like phosphorus, to biological communities like algae and zooplankton. It is crucial that these variables be measured in consistent locations and over consistent time frames, and that comparable sampling and analysis methods are used. Changes in methods are sometime unavoidable, and great effort has been made to document these changes so that any bias introduced by a method change can be accounted for in subsequent trend analysis. Long term monitoring data are invaluable for examining trends in ecosystem variables through time. Observed changes can sometimes be linked to specific events, such as the effect of establishment of zebra and quagga mussels on water clarity, or the effect of upgrades of a waste water treatment plant on phosphorus. In other cases, changes may be more gradual and may be linked to regional stressors like the effect of climate change on temperature and biological communities. These can be more difficult to explain with great certainty. Long term monitoring data can also serve as a baseline to compare localized effects of specific human activities on aquatic ecosystems.

For more detail on specific areas of Severn Sound and inland lakes in the watershed, visit Report and Publications.