Water Quality in the Great Lakes
What makes water safe to drink, swim in, or support aquatic life? The Great Lakes hold 20% of the world's surface freshwater—but their quality isn't guaranteed. From microscopic contaminants to visible algae blooms, water quality affects every living thing in the region. How do we measure it, protect it, and ensure it stays clean for future generations?
Key Quality Parameters
Water quality isn't just about clarity—it's about chemistry, biology, and physics. We test for 45 different parameters, but these eight are the most critical for public health and ecosystem stability.
pH Level
The acidity or alkalinity of water (ideal range: 6.5–8.5). Too low? Corrosion in pipes. Too high? Scale buildup. Both can harm aquatic life.
Dissolved Oxygen
Fish and other aquatic organisms need oxygen to breathe—just like us. Levels below 5 mg/L stress most species. (Cold water holds more oxygen than warm water.)
Turbidity
How cloudy is the water? High turbidity blocks sunlight, smothers fish eggs, and can carry harmful bacteria. Measured in NTU (nephelometric turbidity units).
E. coli Bacteria
A red flag for fecal contamination. One colony-forming unit (CFU) per 100 mL is enough to close a beach. (Yes, that's a single bacterium.)
Nutrients (Nitrogen & Phosphorus)
Too much of a good thing? Excess nutrients fuel algae blooms—like the 2014 Toledo water crisis, which left 500,000 people without drinking water for three days.
Heavy Metals
Lead, mercury, arsenic—these don't break down. They accumulate in fish (and humans). Even low levels can cause neurological damage over time.
Temperature
Warmer water holds less oxygen and speeds up chemical reactions. Climate change is pushing lake temperatures up—Lake Superior's surface has warmed 2.5°C since 1980.
Conductivity
How well does water conduct electricity? High conductivity often means dissolved salts or pollutants—road salt, industrial runoff, or agricultural chemicals.
Testing Methods
From high-tech sensors to old-school titration, our testing methods range from instant results to lab analyses that take days. Here's how we know what's in the water.
Field Testing
Portable kits give us instant readings for pH, dissolved oxygen, turbidity, and conductivity. Our teams carry these to remote locations—like the 300 km of Lake Huron shoreline we monitor annually.
- Multiparameter probes: Test 5+ parameters at once
- Secchi disks: Measure water clarity in seconds
- Colorimeters: Detect nutrients and metals on-site
Lab Analysis
Some tests require precision equipment and sterile conditions. Our Toronto lab processes 1,500 samples monthly—everything from E. coli cultures to mass spectrometry for heavy metals.
- Gas chromatography: Identifies organic pollutants
- Inductively coupled plasma (ICP): Detects metals at parts-per-billion levels
- DNA sequencing: Tracks harmful algae species
Real-Time Monitoring
Buoys and fixed stations send data every 15 minutes—temperature, oxygen, pH, and more. We've got 47 of these "sentinel" stations across the Great Lakes, feeding data to our public dashboard. (You can check it yourself at monitoring.GreatLakesWaterLab.com.)
Pollution Sources
Where does pollution come from? Some sources are obvious—like a factory pipe dumping waste. Others are invisible, like the microplastics in your laundry detergent. Here's the breakdown of what's entering the Great Lakes—and how much.
Agricultural Runoff
Fertilizers and manure wash into lakes during rainstorms. Phosphorus from farms fuels 60% of Lake Erie's algae blooms. (That green sludge? It's not natural.)
Urban Stormwater
Rain picks up oil, heavy metals, and trash from streets—then dumps it into lakes. Toronto's stormwater system releases 1.2 billion liters of untreated runoff yearly.
Industrial Discharge
Factories and refineries release chemicals—some legal, some not. In 2022, we detected PFAS ("forever chemicals") in 92% of Lake Ontario samples near Hamilton.
Wastewater Treatment
Even treated sewage contains traces of pharmaceuticals, microplastics, and nutrients. Ontario's 441 treatment plants release 1.5 trillion liters of effluent annually.
Atmospheric Deposition
Pollution doesn't just come from pipes. Mercury from coal plants and microplastics from tire wear float through the air—then land in lakes.
Invasive Species
Zebra mussels filter water—but they also concentrate pollutants in their bodies. When they die, those toxins re-enter the food chain.
The Invisible Threat: Microplastics
Every laundry load releases 700,000 microfibers. Every tire rotation sheds plastic dust. These particles don't biodegrade—they just break into smaller pieces. We've found microplastics in 100% of Great Lakes fish samples. (Yes, that includes the fish on your plate.)
Treatment Processes
Turning lake water into drinking water isn't magic—it's chemistry, engineering, and a lot of energy. Here's how we do it in Ontario's 12 major treatment plants.
Coagulation & Flocculation
First, we add chemicals like alum to make tiny particles clump together. Think of it as herding cats—except the cats are dirt, bacteria, and algae.
- Alum or ferric chloride added to water
- Particles form "flocs" (visible clumps)
- Process takes 30–60 minutes
Sedimentation
The flocs sink to the bottom of massive tanks. This removes 90–95% of suspended solids. (The sludge at the bottom? That's trucked to landfills.)
- Water flows slowly through sedimentation basins
- Flocs settle as sludge
- Clear water moves to next stage
Filtration
Sand, gravel, and anthracite coal act like a giant coffee filter. We use 1.5 meters of media to catch anything bigger than 0.5 microns. (That's smaller than a red blood cell.)
- Layers of sand, gravel, and coal
- Removes remaining particles
- Backwashed every 24–48 hours
Disinfection
Chlorine kills bacteria and viruses—but too much creates harmful byproducts. We use a mix of chlorine, UV light, and ozone to balance safety and taste.
- Chlorine: 1–2 mg/L residual
- UV light: Inactivates cryptosporidium
- Ozone: Breaks down organic compounds
Advanced Treatment
For contaminants like PFAS or pharmaceuticals, we use:
- Activated carbon: Absorbs organic compounds
- Reverse osmosis: Removes salts and metals
- Ion exchange: Targets specific ions like nitrate
Toronto's R.C. Harris Plant uses all three—processing 1 billion liters daily. (That's enough to fill 400 Olympic swimming pools.)
Safety Standards
Who decides what's "safe"? In Ontario, we follow three sets of standards—provincial, federal, and international. Here's how they compare (and where they fall short).
| Parameter | Ontario (ODWQS) | Canada (Guidelines) | WHO | EPA (USA) |
|---|---|---|---|---|
| E. coli | None detectable | None detectable | 0 CFU/100 mL | 0 CFU/100 mL |
| Lead | 10 µg/L | 5 µg/L | 10 µg/L | 15 µg/L |
| Arsenic | 10 µg/L | 10 µg/L | 10 µg/L | 10 µg/L |
| Nitrate | 10 mg/L | 10 mg/L | 50 mg/L | 10 mg/L |
| PFAS | Not regulated | 200 ng/L (proposed) | Not regulated | 4 ng/L (proposed) |
The PFAS Problem
PFAS (per- and polyfluoroalkyl substances) are in everything from non-stick pans to firefighting foam. They don't break down—and they're linked to cancer, thyroid disease, and immune system damage. Ontario has no standard for PFAS in drinking water. (The U.S. EPA proposed a limit of 4 ng/L in 2023. We're still waiting.)
Who Enforces These Standards?
- Ontario Ministry of the Environment: Sets and enforces provincial standards
- Health Canada: Develops national guidelines
- Municipalities: Test and report water quality (Toronto tests 1,200 samples monthly)
- Great Lakes Water Lab: Independent monitoring and research
In 2022, Ontario issued 127 drinking water violations. Most were minor—but 12 involved E. coli or chemical exceedances. (You can check your local water quality at monitoring.GreatLakesWaterLab.com.)
Monitoring Stations
Where do we get our data? From 1,247 monitoring stations across Ontario—buoys, shoreline labs, and even underwater drones. Here's where they are and what they measure.
Lake Ontario
342 stations. Focus: Urban runoff, industrial discharge, and microplastics. Toronto's Tommy Thompson Park station tracks real-time E. coli levels for beach safety.
Lake Erie
289 stations. Focus: Algae blooms and agricultural runoff. The Pelee Island station has tracked phosphorus levels since 1972—one of the longest continuous records in the world.
Lake Huron
215 stations. Focus: Groundwater intrusion and ship ballast water. The Bruce Peninsula station monitors for invasive zebra mussels.
Lake Superior
198 stations. Focus: Climate change impacts and mining runoff. The Thunder Bay station tracks temperature changes—Lake Superior is warming faster than any other Great Lake.
Lake St. Clair
87 stations. Focus: Wetland health and sediment contamination. The Walpole Island station monitors mercury levels in fish.
Rivers & Tributaries
116 stations. Focus: Agricultural runoff and urban pollution. The Grand River station tracks nitrate levels—critical for downstream drinking water intakes.
How Monitoring Works
Fixed Stations
- Permanent buoys or shoreline labs
- Test 12–24 parameters every 15 minutes
- Data transmitted via cellular or satellite
Mobile Labs
- Vans or boats equipped with testing gear
- Visit 5–10 sites daily
- Test for bacteria, nutrients, and metals
Citizen Science
- Volunteers collect samples monthly
- Test for E. coli, turbidity, and clarity
- Data uploaded to our public dashboard
Underwater Drones
- Autonomous vehicles map lake bottoms
- Test for temperature, oxygen, and contaminants
- Can dive to 300 meters
Real-Time Data Access
All our monitoring data is public. Here's how to access it:
- Interactive map: monitoring.GreatLakesWaterLab.com
- Daily reports: Emailed to subscribers
- API access: For researchers and developers
- Mobile app: "Great Lakes Water Watch" (iOS/Android)
In 2023, our dashboard had 1.2 million visits. (That's a lot of people checking their local water quality.)
What You Can Do
Water quality isn't just our problem—it's everyone's. Here's how you can help protect the Great Lakes.
At Home
- Use phosphate-free detergents
- Reduce lawn fertilizer use
- Dispose of medications properly (not down the drain)
- Wash your car at a commercial car wash (they treat the water)
In Your Community
- Join a shoreline cleanup
- Report pollution to the Spills Action Centre (1-800-268-6060)
- Advocate for green infrastructure (rain gardens, permeable pavement)
- Support local conservation groups
For Businesses
- Implement water recycling systems
- Use non-toxic cleaning products
- Properly store and dispose of chemicals
- Get certified (e.g., WaterSense, EcoLogo)
"I've been testing water in the Great Lakes for 22 years. The biggest change? People care more now. They ask questions, demand data, and want to help. That's how we'll protect these lakes for the next 100 years."
— Dr. Elena Vasquez, Senior Water Quality Scientist, Great Lakes Water Lab