Ontario Nature Blog

Protecting wild species and wild spaces since 1931

It’s cool to be cold: the importance of coldwater streams

Credit: Steven Edwards

The Government of Ontario has identified coldwater streams as a building block for Greenbelt expansion. Here’s why that makes sense.

What are coldwater streams?

It’s not nice when someone gives you the cold shoulder or a cold stare, but when it comes to streams, it’s cool to be cold!

Coldwater streams are fed by groundwater and they remain cold all year. These streams often flow during dry periods because they are not dependent upon precipitation or other surface water.

Coldwater streams are generally less than 19˚C. Healthy cold water streams have native vegetation along their stream banks, fast flowing waters, and habitats such as riffles, pools and runs.

Why are coldwater streams important?

Coldwater streams are important regulators within a watershed. They improve water quality and biodiversity by reducing excess sediment and nutrients from traveling downstream.

Coldwater streams are a hub of biodiversity. They support insects such as mayflies, caddisflies and stoneflies. The juvenile insects can indicate water quality and are also a source of food for fish!

Credit: EcoSpark

Many fish species are restricted to coldwater streams. Brook trout, for example, require a year-round supply of cold water, between 11 ˚C and 16˚C. But increasing stream temperatures have resulted in declining numbers of brook trout. Within the area overseen by the Toronto and Region Conservation Authority, brook trout populations are found in the Duffins Creek, Humber River and Rouge River watersheds, largely restricted to areas overlapping with the Oak Ridges Moraine (a significant headwater feature) and the protected countryside of the Greenbelt.

Another coldwater fish is the endangered redside dace, which thrives in the pools of small streams and headwaters that have a gravely bed. Due to habitat loss, however, redside dace in Ontario are restricted to headwaters primarily in the Greater Toronto Area.

Threats to coldwater streams:

There are several threats to the health of our coldwater streams including:

Urbanization: Increased development causes erosion, sedimentation, and an expansion of impervious surfaces. Together, these can contribute to a rise in stream temperature. In the Credit River, water temperature stations have regularly exceeded their temperature targets between 2004 and 2014.

Climate Change: Water temperature is affected by air temperature. Warmer air results in warmer water.

Commercial use: The use of groundwater for commercial purposes (e.g. municipal, golf-courses, bottled water) reduces the amount available to recharge coldwater streams.

How can we protect coldwater streams?

Even though coldwater streams are a building block in the planned Greenbelt expansion, the government’s  scope is too narrow, leaving out many coldwater streams across the region.

Sign our petition to urge the government to protect all at-risk waters in the Greater Golden Horseshoe.



You can also attend an upcoming open house to show your support for coldwater streams and the protection of our water for future generations.



Joyce Chau is the executive director at EcoSpark, a member of the Oak Ridges Moraine Partnership.


Dufferin County’s Five Best Hikes


Protecting Ontario’s native pollinators where you live


  1. This is an excellent post. In Niagara the Ontario government last year expanded the Greenbelt to include the entire area which supports cold water dependent Brook Trout. This model should be followed in other areas of the province with Brook Trout streams experiencing growth pressures. For more on the Niagara victory, go to my post in the Sierra Club’s own nature blog, Ozone. It features a recent video by Martin Munoz of a beaver swimming in part of the Greenbelt added near my home in St. Catharines.

  2. Harold Wilson

    Too often, cold water streams are deemed expendable by corporate interests intent upon exploiting other resources. In the Rockwood, Ontario area, five years of resident insistence upon a thorough environmental assessment is all that has stood between an aggregate company blasting 30m below the water table to mine limestone and the preservation of a pristine brook trout breeding creek dependant upon the water flowing from the proposed mine. Expansion of the Greenbelt is critical to preserving the very resources all future generations will need: clean air, healthy forests, fertile soil, and the pure, life-giving waters that sustain us all. For more on this epic struggle, visit Concerned Residents Coaliton – No Hidden Quarry on facebook .

Leave a Reply to John Bacher Cancel reply

Sitemap | Privacy Policy | Jobs | My Membership | Contact Us | © Ontario Nature, 2010-2017