Aquatic plants are simply a variety of plants that grow
in water. Aquatic plants supply life-giving qualities to a
lake by providing important shelter, food and nursery
areas for fish and by helping to trap sediments. Because
of their critical role in creating a healthy lake, they are
protected by the Federal Fisheries Act which makes it
illegal to remove or destroy aquatic plants.
When a lake receives an increased amount of nutrients
such as phosphorus, aquatic plants may begin to grow
in over-abundance. This is the case in Lake Simcoe. At
times, aquatic plants can become a nuisance because
they get tangled in boat propellers, they can detract
from swimming and recreation activities, and they wash
up on beaches in large quantities causing unpleasant
odors and aesthetic issues. An even bigger problem
occurs when the plants decay and use up the oxygen
that is vital to the survival of fish.
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.As a result, greater amounts
of phosphorus enter the lake, leading in part to the
abundance in aquatic plants. Recently the lake has also
experienced a marked increase in water clarity due to
the introduction of zebra mussels. The greater water
clarity allows for deeper sunlight penetration, which in
turn allows plants to grow at greater depths, increasing
the habitat available for plant growth.
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
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
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
2008 Research Study –
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
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
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
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
- 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
- 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.