Lake Simcoe Science
Invasive Mussels
Uninvited Lake Dwellers
In the past 200 years close to 150 species of
foreign plants and animals have established
themselves in the Great Lakes Region.
The first foreign species introduced in Lake
Simcoe was the common carp, which escaped
from a Newmarket fish pond in 1896. Since
then, 15 foreign species have colonized the lake,
displacing native plants and animals.
Invasions can happen intentionally through
dumping imported aquarium plants and
animals into rivers, lakes and streams, and
unintentionally, when carried by contaminated
boats and trailers, on fishing gear, or the use of
illegal live bait.
Common invasive species in Lake Simcoe
Three common species found in Lake Simcoe include the round goby (left), common carp (middle) and eurasian watermilfoild (right).
Zebra and Quagga Mussels
A couple of the most well-known "invaders" to Lake Simcoe are zebra mussels and quagga mussels.
Native to the Caspian-Black Sea region of Eurasia, they arrived in the Great Lakes in 1988, carried in the ballast water of container ships. By 1995, zebra mussels had established themselves in Lake Simcoe, followed by quagga mussels in 2004.
While these species look similar, zebra mussels
have a flat side which gives them a distinct
“D” shape. Their shell may have a striped
pattern, but can vary from a solid dark to a pale
appearance. Zebra mussels are typically found
in warm, shallow water.
Quagga mussels, on the other hand, do not have
the flat side and have dark concentric rings on
the shell. Quagga mussels are usually found in
cooler, deeper waters.
Both species live three to five years and start
reproducing about six months after the larvae
become established. A single female zebra or
quagga mussel can produce up to one million
eggs in a growing season.
Where are they found? 
In Lake Simcoe, invasive mussels can be
found on rocks, boulders, and sandy/shell lake
bottoms. Because zebra mussels tend to live
in shallower depths than the quagga mussels,
they are the species most often encountered by
recreational lake users.
In 2009, LSRCA began surveying 747
sites across Lake Simcoe to determine the
distribution of the mussels throughout the lake
and their areas of high concentration.
Both zebra and quagga mussels have been
recorded as deep as 20 metres in much of
Lake Simcoe. Their settlement is restricted by
a change in the lake bed composition to soft
mud and silt, which clogs their filtering ability,
limiting population expansion in these areas.
In Kempenfelt Bay, living zebra and quagga
mussels are found as deep as 31 metres; likely
surviving on food particles that drift off the
steep underwater sides of the bay.
Filtering the Lake
Since 1995, zebra and quagga mussels have
caused colossal environmental changes in Lake
Simcoe.
Like native mussels, they eat algae and nutrientrich bits of sediment. However, these invaders
have an exceptionally high filtering rate, making
them very efficient at removing these important
particles from the water. In fact, zebra and
quagga mussels can filter a volume equivalent
to that of Lake Simcoe every five days!
Before their arrival, residents and lake users
noted the lake water had a “cloudy, greenish”
colour — murky conditions caused by large
amounts of algae in the water, common to lakes
with high phosphorus concentrations. These
particles reduced water clarity in the lake, which
prevented sunlight from reaching deep into the
water column.
With sunlight now penetrating deeper into
the lake, ecological changes have occurred in
nutrient flows, food webs, and habitats of more
aquatic plants.
Zebra & quagga mussels change the
environment of Lake Simcoe
The pictures show a set of four-litre jars filled with murky, water
from the Holland River (left).
Within 10 minutes of the zebra mussels
being added one of the jars (far right), the particles that cause the water
to be murky have been filtered, leaving it clear.
This simple experiment
is a small-scale example of how zebra and quagga mussels have changed
the environment of Lake Simcoe.
Invaders tip the ecological balance
Typically, a change from murky water (usually
due to high algae growth) to clear water is
caused by a decrease in nutrients, such as
phosphorus and nitrogen entering the lake.
While LSRCA has had success in reducing the
amount of phosphorus entering Lake Simcoe,
the clear water is primarily due to the zebra and
quagga mussels.
With zebra and quagga mussels increasing the
clarity of the lake, Lake Simcoe has changed
from a nutrient-rich lake (primarily dominated
by algae) to a plant-dominated lake.
The removal of algae by these mussels means
the excess nutrients that were once taken up by
the algae are now fueling the increased aquatic
plant growth in the lake.
In addition, large quantities of nutrient-rich
waste from zebra mussels is deposited on the
lake bottom each day. These "biodeposits" form
a nutrient-rich substrate, which combined with
increased water clarity, is an ideal environment
for aquatic plants.
Since 1984, the population size of aquatic plants
has tripled.
Lake clarity increases soon after mussels invade
Water clarity measurements at Brechin Monitoring Station from 1980-
2010. Symbols courtesy of Integration and Application Network (IAN)
Symbols and Libraries.
They decrease biodiversity
In addition to changing the natural conditions
of Lake Simcoe, zebra and quagga mussels,
like other invasive species, have changed the
animal community in the lake. Before 1995,
Lake Simcoe was home to 16 species of native
freshwater mussels and clams.
By 2010, only four species were recorded:
zebra mussels, quagga mussels, and very low
numbers of two native species which are at high
risk for local extinction.
Like other invasive species, zebra and quagga
mussels have no natural predators in Lake
Simcoe and can increase rapidly in numbers.
Also, their ability to quickly filter large amounts
of water means they can consume food quicker
than native species.
Change from nutrient-rich lake to
plant-dominated lake
Conceptual drawing illustrates the change from an algae-dominated,
turbid lake to a plant-dominated, clear water lake after mussels invade
Lake Simcoe.
How LSRCA is working to improve the
quality of Lake Simcoe
Once an invasive species enters a lake it is
almost impossible to eradicate it. However,
through our research and monitoring programs,
we now have a better understanding of the
current lake ecosystem and we can determine
what steps we need to take to manage and
prevent new invasive species from being
introduced to the lake.
As part of our lake monitoring program, we
will continue to record how these mussel
populations change from year to year, and
we'll monitor for new invasive species in Lake
Simcoe.
A few key invasive species on our watch list
include Asian (jumping) Carp (now in the
Chicago River close to Lake Michigan), bloody
red shrimp, and aquatic plants like European
water chestnut (currently in several Ontario
lakes), water soldier (recorded in 2012 in the
Trent-Severn waterway), and fanwort.
We work with our many partners, including
our communities, 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
Prevention is the key
You can help by practicing “invasive species
prevention”:
- Do not release aquarium pets or plants, into
waterways or the lake.
- Clean boats, fishing gear, and waders with hot
(at least 50oC) water when moving between
lakes
- Drain bilges and live wells
- Dry boats and equipment (zebra mussels can
live for 10 days out of water!)
- Do not transport bait or water between lakes
