Ontario Gets Specific on Defining Watercourses: Why Is That Important to Your Projects?

By Olivia Robinson – Senior Ecologist and Project Manager

Changes are coming to Ontario’s Conservation Authorities Act. To help you understand how they could impact your projects, I’ve prepared this blog series to break out the key changes from a natural heritage perspective. In the first blog, we explored the origin of the Conservation Authorities Act, the role of Conservation Authorities (CAs), and reviewed what natural hazards are. In part 2, we build off what we learned in Blog 1 by reviewing the changes to the watercourse definition.

Buckle up – this blog gets a bit more technical, but it (hopefully) provides some context in order to help other environmental professionals interpret the latest regulatory changes. I partially wrote this to help me better understand the changes and thought that it may be helpful to share with the broader community. One specific topic that keeps coming up on my projects is the latest change to the watercourse definition, so that is what I have chosen to explore within this blog.

We’ve discussed how the Conservation Authorities Act previously provided definitions for natural hazards. As of April 1, 2024, a new change will include an official updated definition of “watercourse”. Let’s explore this change and its potential implications.

CA mapping typically identifies where surface water drainage features and their potential associated natural hazards could be found. These drainage features could range from seasonal headwater drainage features (defined below) to permanent watercourses, with management requirements dependent upon which. CA mapping of these drainage features is considered a conservative approximation that is intended to be reviewed as part of any proposed development.

What are Drainage Features and How Do They Differ from Watercourses?

Drainage features can be classified either as headwater drainage features (HDFs) or as watercourses. The importance of correctly identifying these features matters because their management differs.

HDFs typically do not have natural hazards associated with them while watercourses could. Note the use of the word typical here, particularly where wetlands are considered. Regulated features (e.g., watercourses) typically have more conservative protections afforded to them in comparison to unregulated features (e.g., swales).

Features with hazards (e.g., watercourses) are regulated by CAs, while features without hazards are reviewed by municipalities.

What are the Proposed Changes?

Under the current Conservation Authorities Act, a watercourse is defined as:

 “an identifiable depression in the ground in which a flow of water regularly or continuously occurs”.

As of April 1, 2024, the refined definition will be:

a defined channel, having a bed and banks or sides, in which a flow of water regularly or continuously occurs”.

In practice, the refined definition will help clarify whether a drainage feature is a headwater drainage feature or a regulated watercourse.

Headwater drainage features are defined within Credit Valley Conservation and Toronto and Region Conservation Authority’s Headwater Drainage Feature Guidelines (2014; subsequently referred to as “the HDF Guideline”) as:

“non-permanently flowing drainage features that may not have defined beds or banks; they are first-order and zero-order intermittent and ephemeral channels, swales and connected headwater wetlands, but do not include rills or furrows”.

By refining the current watercourse definition, and with the definition of headwater drainage feature within the HDF Guideline, this will provide additional clarity as to when a drainage feature is to be considered a regulated watercourse. The previous definition was vague and all-encompassing. This often led to additional protections being provided on drainage features without natural hazards purely on their seasonal conveyance of water. This sometimes limited the potential for management of HDFs within the landscape.

For example, agricultural swales that were mapped as regulated watercourses have sometimes been requested by CAs to be maintained on the landscape within an open corridor, where the HDF Guideline permitted the removal and replication of the feature.

How Will This Change Evaluation Of These Features And What Are The Impacts?

The additional clarity on the definition of watercourse will help consultants and CA staff better understand the following:

  • whether drainage features are considered watercourses within the regulatory of the Conservation Authority, and
  • if they are considered watercourses, how to best regulate these features to preserve and protect their functions on the landscape.

Previously, some drainage features that did not have natural hazards associated with them but had “identifiable depressions” conveying water (e.g., swales) were conservatively managed on the landscape, or permits were required to make alterations in accordance with HDF Guideline recommendations.

Because they met the definition of watercourse, sometimes drainage features were regulated that did not have associated hazards but met the all-encompassing definition. As a result, this conservative approach resulted in delays to project schedules or led to a higher level of protection than necessary for smaller drainage features.

A specific example is an agricultural swale. Swales do not have defined beds and banks and normally do not have natural hazards (e.g., erosion or flood hazards). However, they would sometimes be regulated by CA staff because it was “an identifiable depression” that seasonally conveyed water. This resulted in unnecessary constraints on certain drainage features without regulated hazards.

Now, trained professionals can review the CA mapping to determine where potential watercourses may be. Subsequent field investigation can then determine whether the drainage features have defined bed and bank/sides. Using the CA mapping as a starting point will help identify where potential constraints may be, while allowing for refinement based on feature-specific assessments. And those steps will determine how the feature should be appropriately managed on the landscape.

So how could this impact your project? When evaluating drainage features as part of a development application process, drainage features will either be designated as a regulated watercourse or an HDF. Regulated watercourses (and their natural hazards) will be managed in accordance with CA Act requirements (and its regulation), whereas HDFs will be managed in accordance with the HDF Guidelines.

The Common Misconception: These Changes Will Result In Wide-Spread Removals

CA mapping may continue to highlight drainage features that are HDFs instead of watercourses. This conservative approach will continue ensuring drainage features are being evaluated to determine the best way to manage them on the landscape.

The changes in the watercourse definition will offer appropriate protections and buffers for watercourses, while providing flexibility to apply alternative approaches for drainage features that may not necessarily warrant long-term protection on the landscape.

While this will correctly separate HDFs from the watercourse definition, and result in different management strategies, this does NOT mean that HDFs will not be managed on the landscape. All HDFs will continue to be appropriately managed in accordance with the HDF Guidelines, whether that means that HDFs should :

  • be retained in place with buffers,
  • have their functions replicated (e.g., through low impact development solutions), or
  • be removed all together.

All HDFs (non-regulated drainage features) will continue to be reviewed by municipalities as part of proposed development applications. As these changes move forward in the spring, our team can help evaluate your needs. Contact me if you would like to learn more or discuss this definition of watercourses further. Our next blog will continue to dig deeper into the new combined CA Ontario Regulation (O. Reg. 41/24), including the new prescribed buffers/setbacks and the limits on the conditions that can be attached to CA Act permits.


Credit Valley Conservation and Toronto and Region Conservation Authority. 2014. Evaluation, Classification and Management of Headwater Drainage Feature Guidelines.

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