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Water and Wastewater

Seasonal Shoreline Algae


About Shoreline Algae | Weekly Algae Photos | Shoreline Algae FAQ | A Healthy Lake Ontario

About Shoreline Algae

Cladophora are branched, filamentous green algae that grow in relatively shallow water, significantly contributing to summer odour problems along the lakefront. (Algae are water plants containing chlorophyll. "Algae" is plural; a single plant is an "alga".)

Algae Cladophora
Cladophora is the source of odour in the lake.

Life Cycle of Algae

Cladophora grow quickly in May and June. By July they completely cover the rocky lake bottom to a depth of 10 metres (32 feet) with filaments as tall as 38 centimetres (15 inches).

At this point, the filaments are less firmly attached to the lake bottom and are easily removed by the waves. Strong winds disturb large quantities of algae, creating floating masses that wash up on the shore and decay, causing septic odours. Storms can also clean algae off the beach.

Why Shoreline Algae Grow Along Lake Ontario

  • A shallow, rocky shoreline
    The Lake Ontario shoreline is perfect for Cladophora. Algae on the rocky lake bottom reach over one kilometre from shore to a depth of 10 metres.
  • Water clarity
    Cladophora need light to grow and prefer calm, clear, sunny days. Zebra mussels, originally imported from the Mediterranean in ballast water from ships, filter the water and allow algae to grow at greater depths.
  • Nutrients
    Because algae are plants, they need food to grow. Cladophora can quickly absorb available nutrients in the water. They can also store nutrients, which helps sustain growth should food sources be limited.
  • Temperature
    Cladophora growth depends on the temperature of the lake water. The earlier the water temperature rises in the spring, the more the algae will grow.

When the water temperature reaches 18 - 20 degrees Celsius, Cladophora begin to die. It's these dead, rotting algae that smell, so stronger odours tend to occur in mid-to-late summer, depending on summer temperatures.

Learn More About Algae

For more information on Cladophora, e-mail or call 905-791-7800

Revised: Monday July 06 2015


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