Lake Ontario water colours: What the lake’s hue can tell you

One of my favourite daily rituals in the winter is to check in on the progress of the ice coverage over Lake Ontario. Lake Ontario, from the sky, is midnight blue and lassoed in a delicate thread of turquoise shoreline and pale brown beaches. She’s a beautiful colour. Every time I open up one of NOAA’s satellite images I know that’s my lake.

Up close, standing on the shore, the water washes in clear over Lake Ontario’s sand or gravel beaches.

View from Woodbine Beach, Toronto. (Photo by Lake Ontario Waterkeeper)

But Lake Ontario’s true colour is not always apparent. It can be influenced by many factors that turn it from brown, to turquoise, to gray, and back to blue again.

The colour of the lake can tell us a lot about the lake’s shape, depth, geology, and weather. We can also learn a lot about what is happening in and around the water. Let’s take a look at Lake Ontario’s water colours and see what the different shades can tell us.

Watercolour 101

Blue is water’s signature colour. When light shines on a body of water all the wavelengths of light in the light spectrum are absorbed with the exception of the blues, indigos, and violets. Sometimes green light doesn’t get absorbed either. These unabsorbed colours are what we see. Clouds, sunshine, and shadows do beautiful things to the colour of water, making it appear in different shades of blues, purples, blacks, greys, and greens.

Lake Ontario is a dark shade of blue at its deepest points. The shallower water near the shoreline is lighter, and more brilliant the shades of blue and green become visible.

Suspended and dissolved particles colour the water as well. Suspended particles are things like sediment and algae. Dissolved particles are things like minerals or decaying plant life. The bluer and clearer the water, the less suspended and dissolved particles.

The true colour of a water body is the colour it would be if all suspended particles were removed. The apparent colour of a water body is the colour it is including all of the suspended and dissolved particles.

Lake Ontario can be many colours, and not all of them are signs of good health. These colour swatches can help identify what is behind the colour of the lake. But it’s important to remember that water can be very clear and still have high levels of bacteria and contaminants. On the flip side, water can sometimes be murky and not pose a health risk.

With that in mind, here’s Lake Ontario’s colour guide:

Blues

Lake Ontario, like most dark blue lakes, is deep, cold, and doesn’t have a lot of particles.

Greys and taupes

Water reflects what is happening in the sky. Cloudy, stormy days, like the ones that draw out Lake Ontario’s surfers in the fall and winter, block out the light and cast the water in shades of silver, greys, and mauves.

Greens

The eastern shore of Lake Ontario has many fine white sand beaches, such as at Bluffer’s Park in Scarborough. Water in these areas appear brilliant shades of green and turquoise as the light reflects off the white shallows.

Cloudy green

Green, cloudy water can be a sign of algal growth and chlorophyll-containing algae. This usually means the water has low levels of dissolved oxygen and lots of nutrients. Green water can also be a sign of ongoing contamination from the outfalls. Stormwater outfalls and CSOs are located underwater in most of the slips along Queen’s Quay in Toronto Harbour. The outfalls are a major source of contamination in Toronto's inner harbour.The shade of green can vary depending on the light shining on the water, and the depth of the water, as well as the amount of particles suspended in the water.

Blue-Greens

In certain areas around the lake, the water has a special turquoise colour. The colours can be attributed to the depth of the water and the colour of the sand, clay, and gravel that make up the shoreline.

Cloudy turquoise/aquamarine

Lake Ontario’s colour palette includes dark and light turquoise. In spots where the water contains debris and suspended particles, the colour can become matted and murky.

Neon Green

In 2014, Lake Ontario turned a brilliant shade of neon green. Most people figured that blue-green algae was the culprit. However, scientists concluded the colour was caused by a “whiting event.” Fine particles of calcium carbonate had formed in the water column. Because they are white, they strongly reflected blue and green light. Calcium carbonate forms when there are changes in the water temperature or when the amount of carbon dioxide in the water is reduced due to an increase in photosynthesis by phytoplankton and other microscopic marine life.

Blue-green algae bloom

Blue-green algae blooms can turn the water into a bright green colour. Blue-green algae is a form of bacteria called cyanobacteria. A “bloom” is when blue-green algae reproduce. Blooms like warm temperatures and lots of sunlight. The presence of nutrients in the water, such as phosphorus and nitrogen, speeds up the reproduction process.Blooms usually occur in late summer or early fall. However, certain conditions can cause blooms to ruin our water activities early in the summer. There are several species of cyanobacteria that can produce a number of different toxins (known collectively as cyanotoxins) as the cells die or get eaten by other organisms. Cyanotoxins can cause all kinds of adverse health effects to humans and animals.

Browns

Brown water is usually caused by a combination of combined sewage overflows (CSOs) and contaminated stormwater runoff. Inside Toronto Harbour brown water is typically caused when CSOs in the harbour release sewage. The stormwater outfalls and CSOs are located underwater in most of the slips along Queen’s Quay. During heavy storms contaminated runoff from the Don River also contributes to the brown colour.

Brown water outside of the harbour, is a mix of runoff from the Humber River, bypassed waste from the Humber Wastewater Treatment plant, and stormwater. The Humber runoff and bypass generally flows along the outside of the Toronto Islands. The brown water plume from Toronto has reached as far east as Ajax.

According to Charles Q. Jia, an associate professor in the Department of Chemical Engineering and Applied Chemistry at the University of Toronto, who specializes in air and food waste abatement, “decomposing food waste will give out the brown colour. ”

Sediment runoff such as clay or sand can also change the colour of the water to beige or light brown, especially after heavy rains. Turbulence caused when waves stir up the sand can contribute to the brown colour as well.