A few factors combine to make Lake Simcoe a perfect habitat for aquatic plants: water clarity, an abundance of soft-bottom lake bed habitats for plant roots to attach, and phosphorus and other nutrients entering the lake. Land clearing over the last 200 years, for agricultural and urban development, has upset the natural cycle that moves nutrients like phosphorus through the environment.

​The map (left) shows inputs of phosphorus to Lake Simcoe with the largest amount of phosphorus from the Holland River, resulting in an over abundance of nutrients in Cook’s Bay. 

The diagram below shows how most nutrients enter Lake Simcoe from rivers and surface runoff. 

Natural plant cover (forests and wetlands) retain most of the phosphorus because their roots trap nutrients in the soil, whereas removal of natural cover for urban and agricultural activities results in larger amounts of phosphorus entering waterways from runoff, eventually making its way into the lake.

Diagram showing how plant distribution is connected to phosphorus inputs, sediment type, available light, and the amount of wind and wave exposure.

So what’s the fuss about Phosphorus? 

Nutrients such as phosphorus and nitrogen, which are commonly found in commercial fertilizers and other household products, cause plants to grow. This may seem okay for our lawns and gardens, but these nutrients are also carried into the river and Lake Simcoe – by rainfall, urban runoff, septic systems, lawn clippings, soil and snowmelt – essentially over-fertilizing the water, causing excessive aquatic plant growth.

2008 Research Study – Aquatic plants

To better understand what types of aquatic plants live in Lake Simcoe and areas of high abundance, the Lake Simcoe Region Conservation Authority carries out monitoring and records the number of species. Since our 2008 study, partially funded by Environment Canada through the Lake Simcoe CleanUp Fund, we have recorded 20 plant species, three of which are invasive species, likely brought in by boat traffic.

Aquatic plant cover – Where & Why

The map of our results shows green areas where aquatic plants were found (darker green means more plants). As expected, the nutrient-rich waters and muddy sediment of Cook’s Bay are home to the largest amount of plants. 

While previous studies by the Ministry of the Environment looked only at Cook’s Bay, our 2008 study expanded to the entire lake and mapped four other areas of rich plant growth, including: the waters surrounding Georgina Island at the mouth of the Black River, the eastern shore near the Talbot River, the Ramara shoreline, and offshore from Barrie. These results help us to know where to concentrate our protection and restoration efforts.

Did you know? 

If you weighed all the aquatic plants in Lake Simcoe it would equal 48,000 tonnes. That’s like emptying 1,500 dump trucks into the lake!

Changing Plant Growth in Cook’s Bay 

​Map - Increase in Aquatic Plant Growth from 1984 - 2008

Since early plant studies in Cook’s Bay, there has been a three-fold increase in plants. Plants are growing deeper than before and over a much larger area. 

In 1984, plants were only found in water 6 metres deep or less. Now plants grow as deep as 10 metres. This increase is connected to invasive zebra mussels, which arrived in Lake Simcoe around 1993-94. Zebra mussels feed on algae and particles in the water which makes the water clearer and allows for deeper penetration of sunlight.

Invaders displace native species

The first species foreign to Lake Simcoe arrived in 1896, common carp, which escaped from a fish pond near Newmarket. Since then, at least 15 invasive species, three of which are plants, have been found in Lake Simcoe. 

These invasive species are displacing native species and changing the food web. One of the most striking examples is the aquatic plant: Eurasian watermilfoil, which was first reported around 1984 in a small area of Cook’s Bay near the Maskinonge River. By 2008, Eurasian watermilfoil had increased to become the second most common aquatic plant species. It has displaced native watermilfoil and Muskgrass to occupy much of the shallow, muddy and sandy bottom habitats in Lake Simcoe.

Changes in aquatic plant species cover in Cook's Bay 1984 - 2008

How LSRCA is working to improve the quality of Lake Simcoe 

There is no one cause and no one solution to managing aquatic plants in Lake Simcoe, but it begins with an integrated approach to managing the entire Lake Simcoe watershed. The watershed is a complex and dynamic system that changes over time in response to both human activities and natural events. 

LSRCA works with its many partners, including our communities and municipal, provincial, and federal governments, to protect and restore the environmental health and quality of Lake Simcoe and its watershed. We do this by leading and supporting programs and projects in science and research, protection and restoration, and education and engagement, including: 

• Lake and tributary monitoring
• Subwatershed planning
• Development and testing of new tools and innovative technologies for phosphorus reduction
• Working with landowners to implement restoration projects 
• Public and youth education
  

Small steps add up to big results! 

• A simple step every property owner can take: Don’t mow right to the edge of ditches, streams and river banks. You’ll restore a natural filter, created by grass and native plants that absorbs nutrients before they enter the water. You’ll also protect your property from soil erosion!
  
• Follow tips throughout the newsletter and collect others.
  
• Connect with community and municipal programs.
• Visit the Ontario Ministry of the Environment website to read a copy of the Lake Simcoe Protection Plan​.
  
• Contact our restoration team to learn more about funding opportunities.
  
• Make a donation to our funding partner, the Lake Simcoe Conservation Foundation.