Lake Simcoe Science
A Fish Tale
Fish are Important Measures of
It is widely understood that biodiversity is a
measure of ecosystem health. An ecosystem rich
in biodiversity is more resilient to stressors and
changes, provides better ecosystem services such
as air and water purification, and provides more
resources for recreational, cultural or economic
In the streams, rivers and creeks of the Lake
Simcoe watershed, a key measure of biodiversity
is found in fish populations. As a top predator in
aquatic systems, fish populations respond not only
to direct stressors (such as water quality) but also
to stressors that affect the complex food web that
supports them. Rivers have often been referred
to as a mirror that reflects the health of the
surrounding area. Fish, their primary resident, tells
us a lot about the neighbourhood.
Did you know...
56 species of fish have been captured in Lake Simcoe
tributaries over the last 57 years.
- 39 are native species
- 1 is at risk
- 17 are non-native; 3 are aggressive invaders
Rivers have often been likened to a mirror that reflects the health of the
surrounding area. Fish, their primary resident, tells us a lot about the
Photo of Brook Trout by Larry Halyk
Monitoring fish populations over time
Almost all of the 4,225 kilometres of streams and
rivers in the Lake Simcoe watershed are home
to diverse fish populations. Since 2002, the Lake
Simcoe Region Conservation Authority (LSRCA) has
been monitoring these populations and their habitat
The presence or absence of fish populations and
the numbers found tells us a great deal about the
health of the river. When we capture sensitive
species such as brook trout and mottled sculpin,
it generally indicates that the stream is cold, clean
At sites where we capture species more tolerant
of degraded conditions such as creek chub or an
invasive species like the round goby, we know that
the waters have been negatively impacted.
Annual monitoring tells us if the health of the river
is getting better or worse.
According to Our Research …
The Story is Good
The biodiversity of fish species at a
site tells us how healthy that section
of stream is. Using a scientific tool
known as an Index of Biological
Integrity (IBI) we assign a health
score and compare various stream
systems within the watershed as
well as track changes at sites over
The good news is that the majority
of sites (79%) we monitor in the
Lake Simcoe basin are in “fair” or
“good” condition with only 21% of
the sites scoring a “poor” or “very
Fish Community Health in Lake Simcoe Rivers
The pie charts illustrate the proportion of IBI ratings (health scores) for each subwatershed
within the Lake Simcoe tributaries.
Natural Land Cover Keeps Streams Cool
The subwatersheds with “good”
scores typically have headwaters
originating on the Oak Ridges
Moraine (ORM), such as the East
and West Holland and Pefferlaw
River systems. These areas typically
have more natural land cover and
vegetation along the rivers’ edge
that serve to keep the streams
cool. The buffer of native grasses
and trees filters nutrients such as
phosphorus which soak into the
ground rather than run-off directly
into the water. Because they are on the Oak Ridges Moraine, these sites are also influenced by springs and
groundwater sources that contribute cold, clean water to the system.
Sites that score poorly typically coincide with urban areas where streams have been altered and
experience more extreme flows and stormwater run-off.
We have been monitoring 29 sites across the watershed since 2002. While still a relatively short period
of time from a scientific perspective, trends in the IBI scores show that the majority of the sites (55%)
display stable scores of “fair” while 22% of the sites consistently yield a score of “good”. The stability
of these scores over the last 10 years tells us that the fish
communities have remained relatively unchanged. Of the
remaining sites, 13% showed a trend of getting better and 10%
showed a trend of getting worse.
While the IBI is a measure of overall diversity, there are a few
key species that have a greater impact on the score. A number of
the sites showing an improving trend are related to the capture
of brook trout where they were not captured before. Conversely,
declining trends are linked to sites where brook trout are no
longer captured or where invasive species such as the round goby
have begun to be captured.
From an ecosystem health
Fish communities in our watershed have
remained relatively stable over the past 10
years, with only 10% of the sites we monitor
showing a declining trend.
Brook Trout: The Fresh Water Equivalent of the Canary in the Coal Mine
Generally only the healthiest tributaries
in the Lake Simcoe watershed can
support brook trout, as they have specific
requirements including the need for cold,
clear water and gravel bottoms. Brook
trout prefer water temperatures between
13OC and 18OC and are highly sensitive
to even small changes in temperature,
oxygen levels, pH levels, or decreases in
Because of their environmental sensitivity,
we typically find the majority of brook
trout in the cold, fast flowing headwater
streams on or near the Oak Ridges and
Oro Moraines. It is rare to find brook
trout in highly urbanized areas. A notable
exception to this is the City of Barrie,
where populations are still being found.
We believe that their continued survival
in Barrie is due to the strong groundwater
upwellings in the streams that serve to
keep the water cold. We are working with
the City of Barrie to maintain and, where
possible, enhance the habitat for this
Brook Trout and Mottled Sculpin Capture Sites
Brook Trout are found predominantly in the headwaters on or near the Oak
Ridges and Oro Moraines. Mottled Sculpin, having slightly less stringent habitat
requirements, show a greater distribution throughout the watershed and serve
as an indication where restoration ef forts could pave the way for brook trout reestablishment.
Bringing Brook Trout Back
Mottled sculpin also live in the cool and
cold water streams of the Lake Simcoe
watershed, although they are more
tolerant of warmer temperatures than
brook trout. Streams supporting only
mottled sculpin are therefore considered
good areas to focus restoration efforts
since they have the best chance of once
again supporting a brook trout population. One such area identified is in the smaller tributaries of the
Beaver River (in the central east section of the watershed).
The presence of mottled sculpin is one indicator that restoration efforts
could bring back brook trout to areas they may have abandoned.
The return of brook trout to an area where we’ve undertaken restoration, is just one indication that our
efforts have been successful.
Trouble Spot: The Invasive Round Goby
The round goby is an invasive species of great
concern. Populations were first discovered in our
watershed in the Pefferlaw River in 2004, likely
brought in through the release of live bait. In 2005
unsuccessful efforts were made to eradicate them.
They have since spread throughout Lake Simcoe.
Round Goby (Neogobius melanostomus) Photo Credit: Larry Blight
Round gobies are an aggressive species that
reproduce quickly and feed on the eggs of native
species, therefore outcompeting them.
Invasive species populations impact watershed
health (IBI) scores. The presence of the goby in the
Pefferlaw River has caused the IBI score to go from
“good” to “fair” in just six years. With their spread
through the lake, gobies have recently been caught
in the mouths of many other river systems and we
are likely to see additional IBI declines as a result.
Round goby expansion into the mid reaches and
headwaters of Lake Simcoe tributaries will largely be
prevented by existing barriers, such as dams, that
will block their progress. However, anglers still have
a role to play in preventing their further spread by
following best practices such as not releasing live
The failure to eradicate the round goby in our
watershed illustrates the importance of prevention.
Most invasive species are introduced as a result
of human activities. Once an invader arrives, it is
extremely difficult to eliminate.
Preventing the Spread of Invasive Species
- Dispose of live bait in the trash, not in the
- Take unwanted aquarium fish or plants back to
your local aquarium store.
- Clean your boat after bringing it out of the lake,
especially if moving to another body of water.
How LSRCA is working to improve the
quality of Lake Simcoe
We are working to improve fish habitat in our
watershed through the implementation of
improvement projects, which range from riparian
plantings to stream realignments and barrier
removals. These efforts improve water quality, create
or enhance habitat, and allow fish passage into areas
where they have been previously restricted thereby
improving diversity throughout the system.
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.
- Lake and tributary monitoring
- Subwatershed planning
- Development and testing of new tools
and innovative technologies for phosphorus
- Working with landowners to implement
- Public and youth education