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The Changing Waters of Georgian Bay

This year we celebrate our 20th Anniversary! In 2004, Georgian Bay Biosphere (GBB) was recognized by UNESCO as a globally ecologically significant region with the potential to promote sustainable development – striving for “a balance between people and nature.” Good water quality is essential for ecosystem health and human enjoyment. Without clean water, aquatic food webs suffer and many of our favourite summer activities are compromised. As the largest freshwater archipelago in the world, monitoring water quality and sharing key issues and threats to Georgian Bay is a big part of our work.

Since 2013, we have been involved in supporting and reporting on various indicators of water quality. In 2023, we tested water quality at 22 sites across the Biosphere region, our most ever!

Our State of the Bay ecosystem health program began in 2008 as a way to gather the best available research about water, wetlands, fisheries, and habitats in this unique landscape and share trends and recommendations with those who want to take action. As part of the program, we hold conferences and workshops along the coast, deliver classroom lessons, and release a magazine every five years.

In 2023, we released our third edition of State of the Bay! The magazine provides an overview of the health of eastern Georgian Bay, sharing information about key issues and threats and weaving Anishinaabek perspectives throughout.

The latest edition detailed numerous changes observed in the waters of Georgian Bay and inland lakes in the last several decades. Here is a summary of three notable changes.

Decline in Offshore Total Phosphorus Concentrations

The nutrient phosphorus is the foundation of life in the waters of Georgian Bay and inland lakes. Phosphorus feeds the smallest organisms (e.g., algae) which in turn feed zooplankton, prey fish, and predator fish.

In the deep offshore waters of Georgian Bay, phosphorus levels have naturally been low. However, long-term trends show significant total phosphorus (TP) declines, with the most dramatic declines observed since the mid- to late-1990s. This decline is believed to be linked, in part, to the introduction of invasive zebra and quagga mussels.

TP concentrations have since levelled out at around two micrograms per litre, but this low-nutrient environment means the offshore waters of Georgian Bay can no longer support the same abundance and diversity of species they once did.

Water Level Fluctuations

The past 20 years have brought record highs (2020) and lows (2013) in Georgian Bay water levels. Seasonal and annual water level fluctuations are a normal part of life on the Bay and are important for maintaining healthy coastal wetlands and biodiversity. However, sustained extreme high or low water levels can have negative impacts on some habitats and species, not to mention shoreline properties.

Environment and Climate Change Canada recently conducted an extensive study to better understand the resiliency of Great Lakes coastal wetlands to changes brought on by the impacts of climate change, including varying water levels. In general, the study found that wetlands in eastern Georgian Bay showed greater vulnerability to the effects of climate change under higher water levels when compared to the same wetlands under more stable or lower water levels.

Increasing Chloride Levels

Chloride levels measured in Ontario waterbodies near or downstream of areas of road salt application (winter-maintained roads, residential areas, near businesses) are rising.

In the Muskoka River Watershed, which empties into Georgian Bay, eight locations were sampled monthly for one year in 1983 and again 35 years later. The sampling locations range from areas high in the watershed with less development and roads, to the lower, more developed end of the watershed. The results show that as you move downstream through the watershed, chloride and sodium levels increase. While other indicators of water quality have improved over the last 35 years, chloride levels have almost doubled in the lower, more developed reaches of the watershed. Similarly, chloride levels in undeveloped lakes have fallen, whereas in developed lakes with nearby winter-maintained roads, chloride levels have increased.

Read the magazine to understand the changes scientists and communities have observed, what Indigenous perspectives can help us learn, and how you can get involved in local stewardship efforts. Find it online at or free throughout the region.

To become a Biosphere member, make a 20th anniversary donation, or learn about upcoming events, visit

Biosphere staff conducted water quality monitoring at 22 sites across
the region in 2023
Mishiikenh Kwe (Autumn Smith) speaking about their artwork titled Seasons, created for the centrefold of the 2023 State of the Bay magazine. Mishiikenh Kwe is an Anishinaabe (Ojibwe and Odawa) woodland artist living in Magnetawan First Nation.
Biosphere staff performing an oxygen test.

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