Free public reference · Updated for 2026 season · Data-backed
GTA Mosquito & Tick
Pressure Map 2026
Pressure scores for every GTA city, calculated from Public Health Ontario tick surveillance data, geographic features (ravines, wetlands, escarpment), and 200+ BuzzSkito property assessments since 2024.
Quick Answer
Which GTA city has the worst mosquito and tick pressure?
Toronto, Hamilton, Burlington, and Caledon are the four highest-pressure cities in the Greater Toronto Area for 2026, each scoring 88–92 out of 100 on the GTA Pressure Index. Toronto’s Don Valley ravine network (largest urban ravine system in North America), Hamilton’s Cootes Paradise wetlands + Niagara Escarpment, Burlington’s escarpment edge, and Caledon’s Oak Ridges Moraine all create severe mosquito and tick conditions. Mississauga, Oakville, Halton Hills, Milton, Scarborough, and Markham score in the high range (76–82). Brampton, Vaughan, Richmond Hill, North York, Etobicoke, Woodbridge, Kleinburg, King City, and Georgetown score moderate (57–68). Thornhill is the only GTA city in the lower-pressure tier (52). Within any city, individual properties swing ±30 points based on neighbourhood and yard features — see your specific property’s score below.
Pressure tiers across the GTA
Sorted from highest to lowest. Click any city to expand its profile, top neighbourhoods, and peak weeks.
92Toronto
SEVERE pressure
Toronto
SEVERE pressure
Primary pressure driver
Don Valley ravine system + Humber/Don river corridors
Top high-pressure neighbourhoods
High Park · Rosedale · Forest Hill · Leaside · East York · The Beaches · Riverdale
Peak risk window
Jun 13 – Aug 22
⚠️ Lyme-relevant tick density
Public Health Ontario flags this area for blacklegged tick surveillance.
Toronto contains the largest urban ravine network in North America (11,000+ acres). Properties within 500m of any ravine see 3-5x average city pressure.
90Hamilton
SEVERE pressure
Hamilton
SEVERE pressure
Primary pressure driver
Niagara Escarpment forests + Cootes Paradise wetlands
Top high-pressure neighbourhoods
Stoney Creek · Dundas · Ancaster · Waterdown · Flamborough
Peak risk window
Jun 8 – Aug 17
⚠️ Lyme-relevant tick density
Public Health Ontario flags this area for blacklegged tick surveillance.
Hamilton sits at the junction of the escarpment, Cootes Paradise (one of Ontario's largest urban wetlands), and the Beverly Swamp. Highest combined mosquito + tick burden of any GTA city.
89Burlington
SEVERE pressure
Burlington
SEVERE pressure
Primary pressure driver
Cootes Paradise + Mount Nemo Escarpment
Top high-pressure neighbourhoods
Aldershot · Tyandaga · Roseland · Millcroft · Orchard
Peak risk window
Jun 13 – Aug 22
⚠️ Lyme-relevant tick density
Public Health Ontario flags this area for blacklegged tick surveillance.
Lakefront + escarpment double-pressure. Tyandaga and Aldershot are particularly high — escarpment forests + Cootes Paradise within 1 km.
88Caledon
SEVERE pressure
Caledon
SEVERE pressure
Primary pressure driver
Oak Ridges Moraine + Forks of the Credit
Top high-pressure neighbourhoods
Caledon East · Bolton · Inglewood · Belfountain
Peak risk window
Jun 5 – Aug 14
⚠️ Lyme-relevant tick density
Public Health Ontario flags this area for blacklegged tick surveillance.
Oak Ridges Moraine is one of Ontario's highest blacklegged tick density zones. Caledon East area flagged by Public Health Ontario as Lyme-endemic since 2019.
82Mississauga
HIGH pressure
Mississauga
HIGH pressure
Primary pressure driver
Credit River corridor + Rattray Marsh
Top high-pressure neighbourhoods
Streetsville · Meadowvale · Erin Mills · Port Credit · Lorne Park · Cooksville
Peak risk window
Jun 13 – Aug 22
⚠️ Lyme-relevant tick density
Public Health Ontario flags this area for blacklegged tick surveillance.
Credit River runs the full length of the city. Properties within 500m of the river see 3-5x city-average mosquito populations from May to October.
81Oakville
HIGH pressure
Oakville
HIGH pressure
Primary pressure driver
Sixteen Mile Creek + Bronte Creek + Lake Ontario humidity
Top high-pressure neighbourhoods
Bronte · Glen Abbey · Joshua Creek · River Oaks · Eastlake · West Oak Trails
Peak risk window
Jun 13 – Aug 22
⚠️ Lyme-relevant tick density
Public Health Ontario flags this area for blacklegged tick surveillance.
Two major creek systems plus lakefront humidity extend the mosquito season 1-2 weeks longer than inland properties. Bronte Creek Provincial Park drives heavy tick pressure for adjacent neighbourhoods.
79Halton Hills
HIGH pressure
Halton Hills
HIGH pressure
Primary pressure driver
Niagara Escarpment + Bruce Trail + Hilton Falls
Top high-pressure neighbourhoods
Georgetown · Acton · Glen Williams
Peak risk window
Jun 5 – Aug 14
⚠️ Lyme-relevant tick density
Public Health Ontario flags this area for blacklegged tick surveillance.
Bruce Trail and Hilton Falls Conservation Area drive significant tick pressure across the municipality. Inland location means slightly earlier season than lakefront cities.
78Milton
HIGH pressure
Milton
HIGH pressure
Primary pressure driver
Niagara Escarpment edge + Crawford Lake + Halton Greenbelt
Top high-pressure neighbourhoods
Old Milton · Beaty · Coates · Willmott · Scott · Bowes
Peak risk window
Jun 8 – Aug 17
⚠️ Lyme-relevant tick density
Public Health Ontario flags this area for blacklegged tick surveillance.
Mount Nemo, Rattlesnake Point, and Crawford Lake conservation areas border Milton. Properties on the western edge see escarpment pressure equivalent to Burlington.
78Scarborough
HIGH pressure
Scarborough
HIGH pressure
Primary pressure driver
Rouge National Urban Park + Highland Creek
Top high-pressure neighbourhoods
Rouge · Centennial · Guildwood · West Hill · Morningside
Peak risk window
Jun 13 – Aug 22
⚠️ Lyme-relevant tick density
Public Health Ontario flags this area for blacklegged tick surveillance.
Rouge National Urban Park (over 79 km²) is the largest urban park in Canada and a confirmed tick reservoir. Eastern Scarborough properties see the highest tick burden in the GTA.
76Markham
HIGH pressure
Markham
HIGH pressure
Primary pressure driver
Rouge National Urban Park watershed
Top high-pressure neighbourhoods
Unionville · Cornell · Markham Village · Box Grove · Cathedraltown
Peak risk window
Jun 8 – Aug 17
⚠️ Lyme-relevant tick density
Public Health Ontario flags this area for blacklegged tick surveillance.
Western Markham is moderate; eastern Markham (closer to Rouge Park) flips to high. Box Grove and Cornell are particularly affected.
68Brampton
MODERATE pressure
Brampton
MODERATE pressure
Primary pressure driver
Humber River + Etobicoke Creek + Heart Lake
Top high-pressure neighbourhoods
Heart Lake · Castlemore · Springdale · Mount Pleasant · Bramalea · Fletcher's Meadow
Peak risk window
Jun 8 – Aug 17
⚠️ Lyme-relevant tick density
Public Health Ontario flags this area for blacklegged tick surveillance.
Multiple creek and stormwater pond systems create variable pressure across the city. Heart Lake area is severe; downtown Brampton is moderate.
67Vaughan
MODERATE pressure
Vaughan
MODERATE pressure
Primary pressure driver
Humber River + Don River West
Top high-pressure neighbourhoods
Kleinburg · Maple · Concord · Woodbridge
Peak risk window
Jun 8 – Aug 17
Mostly suburban, but Kleinburg estate properties on the Humber River edge see pressure equivalent to Mississauga's Credit River corridor.
66Richmond Hill
MODERATE pressure
Richmond Hill
MODERATE pressure
Primary pressure driver
Oak Ridges Moraine (north) + Rouge River
Top high-pressure neighbourhoods
Oak Ridges · Bayview Hill · South Richvale
Peak risk window
Jun 8 – Aug 17
⚠️ Lyme-relevant tick density
Public Health Ontario flags this area for blacklegged tick surveillance.
Northern Richmond Hill is on the Oak Ridges Moraine — high tick density. Southern Richmond Hill is suburban moderate.
64North York
MODERATE pressure
North York
MODERATE pressure
Primary pressure driver
Don River West Branch + Black Creek
Top high-pressure neighbourhoods
Willowdale · York Mills · Don Mills · Bridle Path
Peak risk window
Jun 13 – Aug 22
Properties along Don River West see ravine-equivalent pressure. Bridle Path estates with mature canopy and creek access flip to high.
62Etobicoke
MODERATE pressure
Etobicoke
MODERATE pressure
Primary pressure driver
Humber River corridor
Top high-pressure neighbourhoods
The Kingsway · Mimico · Long Branch · Etobicoke Creek
Peak risk window
Jun 13 – Aug 22
Western Etobicoke along the Humber River sees significant pressure. Eastern lakefront flats are lower.
61Woodbridge
MODERATE pressure
Woodbridge
MODERATE pressure
Primary pressure driver
Humber River corridor
Top high-pressure neighbourhoods
Sonoma Heights · West Woodbridge · East Woodbridge
Peak risk window
Jun 8 – Aug 17
Suburban with the Humber running through — pressure varies sharply by lot proximity to the river.
60Kleinburg
MODERATE pressure
Kleinburg
MODERATE pressure
Primary pressure driver
Humber River valley estate setting
Top high-pressure neighbourhoods
Kleinburg Village · Copperwood
Peak risk window
Jun 8 – Aug 17
⚠️ Lyme-relevant tick density
Public Health Ontario flags this area for blacklegged tick surveillance.
Estate properties on large lots adjacent to the Humber. River-front properties flip to high pressure.
58King City
MODERATE pressure
King City
MODERATE pressure
Primary pressure driver
Oak Ridges Moraine forests
Top high-pressure neighbourhoods
King City · Schomberg · Nobleton
Peak risk window
Jun 5 – Aug 14
⚠️ Lyme-relevant tick density
Public Health Ontario flags this area for blacklegged tick surveillance.
Moraine forests support high tick density relative to city average. Mosquitoes are moderate; ticks are the bigger concern.
57Georgetown
MODERATE pressure
Georgetown
MODERATE pressure
Primary pressure driver
Credit River edge + Hungry Hollow ravine
Top high-pressure neighbourhoods
Glen Williams · Park District · Devereux
Peak risk window
Jun 5 – Aug 14
Most properties are suburban-moderate. Properties adjacent to Hungry Hollow or the Credit River edge are high.
52Thornhill
LOWER pressure
Thornhill
LOWER pressure
Primary pressure driver
Bayview ravines + Pomona Mills Park
Top high-pressure neighbourhoods
Royal Orchard · Beverley Glen · German Mills
Peak risk window
Jun 13 – Aug 22
Mostly suburban with localized ravine pressure. Bayview-adjacent properties flip moderate.
Free 60-second tool
City averages don’t tell your yard’s story.
A “moderate” Brampton home backing onto Heart Lake outscores a “severe” Toronto home in an open neighbourhood. Get your specific 1-100 pressure score based on your address, lot, and yard features.
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How GTA pressure scores are calculated
The GTA Mosquito & Tick Pressure Index combines four input categories. Scores are calibrated against observed pressure at BuzzSkito-treated properties and cross-referenced with Public Health Ontario tick surveillance data updated annually.
1. Permanent flowing water proximity
Rivers and major creeks support continuous mosquito breeding from May through October. The Credit River, Don Valley system, Humber River, Sixteen Mile Creek, Bronte Creek, and Etobicoke Creek are the largest contributors. Properties within 500m of permanent flowing water see 3–5x average city pressure.
2. Standing water and wetland systems
Cootes Paradise, Beverly Swamp, Heart Lake Conservation Area, Rattray Marsh, and dozens of stormwater management ponds across the GTA produce localized severe mosquito populations. Stormwater ponds in particular are an under-recognized driver in newer suburban neighbourhoods.
3. Tree canopy and humidity microclimate
Mature tree canopy + lake-adjacent humidity creates the still-air resting habitat adult mosquitoes prefer during the day. Toronto’s Old Forest neighbourhoods (Forest Hill, Rosedale, Lawrence Park) and Mississauga’s Lorne Park / Mineola see canopy-driven elevated pressure regardless of water proximity.
4. Public Health Ontario tick surveillance data
PHO publishes annual blacklegged tick (Ixodes scapularis) surveillance reports identifying Lyme-endemic zones. The four GTA Lyme-endemic zones are: Oak Ridges Moraine (Caledon, King City, north Richmond Hill); Rouge National Urban Park (Scarborough, east Markham); Niagara Escarpment edge (Burlington, Halton Hills, Milton); and the Hamilton-Wentworth conservation lands. Cities containing or bordering these zones have elevated tick scores.
Why pressure varies dramatically within a single city
A “moderate” Brampton score reflects a city average — but Heart Lake-adjacent properties in north Brampton score in the severe range, while open suburban lots in Mount Pleasant score in the lower range. The city average is useful for general planning, but actual property pressure can swing 30+ points based on:
- Distance to nearest flowing water (river or major creek)
- Distance to standing water (pond, conservation wetland, stormwater pond)
- Lot vegetation density (wooded vs. open)
- Proximity to ravine systems
- Neighbouring property water features (a neighbour’s pond affects you)
For an actual property-level score, the free 60-second yard risk assessment calculates your specific 1-100 score based on your address, lot, features, and family situation.
Sources & methodology
- Public Health Ontario — Lyme Disease Active Tick Surveillance
- PHO — West Nile Virus surveillance
- CDC — Lyme Disease (cross-border tick density data)
- eTick.ca — citizen-science tick identification (Bishop’s University)
- 200+ BuzzSkito property assessments across the 19 GTA cities (proprietary data, May 2024 – May 2026)
This map is updated annually before the start of each mosquito season. Last updated May 2026 for the 2026 season. Pressure scores are advisory only — for medical concerns about Lyme disease or West Nile virus, contact your local public health unit.
Frequently Asked Questions
What is the GTA Mosquito Pressure Map?
A free public reference showing mosquito and tick pressure levels for every city in the Greater Toronto Area, calculated from a combination of geographic factors (ravine systems, water sources, conservation areas, escarpment proximity), Public Health Ontario tick surveillance data, and observed pressure across 200+ GTA properties BuzzSkito has assessed since 2024. Updated annually for the May–September season.
How is GTA mosquito pressure calculated?
Pressure scores combine four data inputs: (1) proximity to permanent flowing water (rivers, creeks) which sustains continuous breeding May through October; (2) proximity to standing water sources (ponds, wetlands, conservation areas); (3) tree canopy and humidity microclimate factors; (4) Public Health Ontario tick surveillance data for blacklegged tick density. The result is a 0-100 score, where any score above 75 represents above-average pressure for the GTA.
Which GTA city has the worst mosquito problem?
Toronto, Hamilton, Burlington, and Caledon are tied at the top of the pressure index — each for different reasons. Toronto's Don Valley ravine system is the largest urban mosquito reservoir in any North American city. Hamilton sits at the convergence of the Niagara Escarpment, Cootes Paradise wetlands, and the Beverly Swamp. Burlington has Cootes Paradise plus the Mount Nemo Escarpment edge. Caledon contains the Oak Ridges Moraine — one of Ontario's highest blacklegged tick density zones.
Where in the GTA are ticks the worst?
Public Health Ontario tick surveillance flags four GTA zones as Lyme-endemic: (1) Oak Ridges Moraine (Caledon, King City, north Richmond Hill); (2) Rouge National Urban Park (Scarborough, east Markham); (3) Niagara Escarpment edge (Burlington, Halton Hills, Milton); (4) Hamilton-Wentworth conservation lands. Properties within 500m of any of these zones see significantly elevated blacklegged tick burden.
How accurate are the pressure scores?
Scores are calibrated against observed mosquito pressure at 200+ BuzzSkito-assessed properties since 2024 and validated against Public Health Ontario tick surveillance reports. Within each city the score represents an average — individual properties can swing 30+ points based on neighbourhood and yard features. The free yard risk assessment at /yard-risk-report calculates the actual score for any specific GTA address using the same methodology applied to your individual property factors.
When does mosquito season start in the GTA?
Mosquito activity in the GTA typically begins late April when daytime temperatures consistently exceed 10°C. Peak activity runs early June through mid-August. Lake-adjacent cities (Toronto, Mississauga, Oakville, Burlington) have a 1-2 week longer season because Lake Ontario humidity sustains pressure into late September. Inland cities (Caledon, King City, Halton Hills) front-load their season with peak activity in late May and a smaller late-August surge.