Skip to contentOntario.caFrançais

• Why Lake Simcoe is important
• Why its health is at risk
• How phosphorus impacts the lake's health
• Where this extra phosphorus comes from
• Taking action: What Ontario is doing and what you can do to protect Lake Simcoe
• Our partners

Why Lake Simcoe is important 

Lake Simcoe is the largest inland lake in southern Ontario, outside of the Great Lakes, and its watershed is home to 350,000 people. Besides a beautiful natural environment, the area is also a valuable economic asset for the province. For example:

• The lake is a valuable sport fishery and recreational asset, which contributes about $200 million per year to the province's economy.
• Almost half the watershed area is agricultural land, with approximately 2,000 farms that generate about $300 million per year.

Why its health is at risk 

The Lake Simcoe watershed has experienced a wide range of interrelated pressures affecting the watershed – excessive nutrients, pollutants, invasive species, impacts of climate change and increasing pressures from human activities.

The last four decades of research, monitoring, and scientific studies show how human-related activities, including urban and rural uses, recreation and agriculture, have impaired the health of the Lake Simcoe watershed ecosystem through direct and indirect changes. The threats include:

• degraded water quality due to excessive nutrients, such as phosphorus, contaminants and pathogens, that directly or indirectly affect the health of the ecosystem and the suitability of the water for recreational uses
• newly introduced species, such as zebra mussels, that compromise the condition and equilibrium of the ecosystem and its resistance to other stresses
• emerging threats, such as climate change, that also affect the condition, equilibrium, and resistance of the ecosystem
• loss and fragmentation of sensitive natural areas and habitat, such as shorelines, wetlands, streamside areas, or forested lands, directly affecting the health of the watershed ecosystem
• water quantity changes that alter ecosystem function, the quality and availability of aquatic habitats, as well as the amount of water available for human uses
• other human pressures, such as fishing and other resource uses, that may remove key resources from the ecosystem beyond its capacity to replenish itself

Some of these challenges are not unique to this lake, but Lake Simcoe has particular characteristics that need a targeted plan to address its specific needs.

How phosphorus impacts the lake's health 

One significant concern affecting Lake Simcoe's ecological health is an over-abundance of phosphorus. Some phosphorus is important to ecosystem health, but too much of it causes plants and algae in the lake to grow excessively. When these plants eventually decay, they use up a lot of the water's oxygen, leaving the lake's fish with less and less of the oxygen they need.

Currently, the cold-water fishery is no longer self-sustaining, water quality has been impacted and the landscape has lost some of its natural features.

Where this extra phosphorus comes from 

Phosphorus is a natural substance found in rocks and soil, and is a key nutrient for plants. The trouble is, after two centuries of human activity and community growth in the area, too much phosphorus is entering Lake Simcoe from sewage plants, storm sewers, septic systems, urban and agricultural run-off, and airborne particles.

Taking action: What Ontario is doing and what you can do to protect Lake Simcoe 

The Ministry of the Environment is privileged to lead a multi-ministry team on behalf of the provincial government. We invite you to explore this section of our site to learn how we're protecting its health. Find out about:

• how to get involved in shaping the actions we're taking and how to take your own action
• laws, plans and strategies protecting Lake Simcoe
• mapping and monitoring the Lake Simcoe watershed and its subwatersheds
• the expert committees who help ensure we meet all stakeholder needs and concerns
• training for community members, engineers, conservation authority and municipal planners, and other interested parties to implement land-use and development-related policies
• the progress we've made

Our partners

The Lake Simcoe Protection Plan is a product of collaboration and partnerships among many agencies and ministries including:

• Ministry of Environment
• Ministry of Natural  Resources
• Ministry of Agriculture, Food and Rural Affairs
• Ministry of Municipal Affairs and Housing
• Lake Simcoe Region Conservation Authority