Thunder Bay Hydro Coporation

Serving the City of Thunder Bay with electricity.

Tree Trimming

Home > Support > Safety > Tree Trimming


Trees planted under power lines can grow to be a hazard. Not only can they be the cause of power outages, they can also endanger adventurous, tree-climbing children.

Why Does Thunder Bay Hydro Trim Trees?

Thunder Bay Hydro has an aggressive tree trimming program that maintains and removes trees and limbs along utility easements to prevent contact with high voltage electrical wires. The purpose of the program is to ensure public safety and to provide a reliable electrical service to all of our customers by preventing unscheduled power interruptions.


Anyone who prunes or climbs trees that are in contact with the power lines is putting themselves into potentially highly dangerous situations.

Trees and the ground around them may become energized when branches come into contact with the power lines.

Momentary contact between the tree and energized power lines could be fatal to anyone who is in proximity of the tree.


Trees are a significant cause of power outages. Outages from trees are caused from branches rubbing on power lines, branches falling on power lines and trees falling across power lines during storms.

By trimming power lines on a regular schedule to a minimum clearance, Thunder Bay Hydro will eliminate predictable safety hazards and reduce tree related outages. 

Utilities' Access to Private Property

The Electricity Act grants access for Thunder Bay Hydro to “enter and maintain any land for the purpose of cutting down or removing trees, branches or other obstructions”.

Easements are established at the municipal development planning stage that allows Thunder Bay Hydro and other utilities to access and maintain equipment on private properties. In addition, homeowners and private businesses are required to sign a “Terms of Agreement” with Thunder Bay Hydro that agrees to allow access for maintenance before service connections are made.


The 1998, Electricity Act of Ontario requires that Thunder Bay Hydro maintain trees and brush to minimum clearances around its power lines. It also grants access for Thunder Bay Hydro to “enter and maintain any land for the purpose of cutting down or removing trees, branches or other  obstructions”.  

Ontario’s Occupational Health and Safety Act and Regulations stipulate what those clearances are and what the “Safe Limits of Approach” are for trained and untrained persons.

Homeowners and private businesses are required to sign a “Terms of Agreement” with Thunder Bay Hydro that agrees to allow access for maintenance before service connections are made.

City of Thunder Bay By-law 008-2005 specifies that conifers on city-owned property must be removed.

Responsibilities and Qualifications

Minimum clearances are required between power lines and trees, branches and foliage. Homeowners are responsible to keep trees clear of the service line that runs into their homes.

Thunder Bay Hydro has the responsibility and the training to trim or remove trees inside of the power line corridor.


Thunder Bay Hydro will only remove trees outside of the power corridor when these trees could fall into the line and create a hazard.

Staff Qualifications

Thunder Bay Hydro uses highly skilled and specially trained staff and contractors to conduct any work inside the power corridor.

Trees are trimmed to International Society of Arboriculture and the ANSI A300 Standards. These are also the standards that the City of Thunder Bay follows for tree work.

Clean Up

When a Thunder Bay Hydro crew or an approved contractor is conducting tree trimming or line clearing during regular maintenance, limbs, branches and other debris will normally be removed from the property.

In the event of a removal of a tree, larger pieces will be cut into manageable lengths and left for the homeowner's use or disposal. 

Storm Damage

When trees and branches are cleared from power lines due to storm damage, emergency crews will not clean up the debris but will leave it for disposal by the property owner.


Why Not Just Lop off the Top?

Topping creates poor tree form that is weaker and more susceptible to disease and wind damage. Topping causes stress to the tree by significantly reducing the trees ability to produce food.The tree reacts by activating dormant multiple buds that create poorly attached branches that require more frequent pruning.



This will eventually lead to further conflicts between the tree and the power lines. The City of Thunder Bay has passed a By-law that stipulates that City conifers (those growing on city-owned property) must not be topped.  They will be removed.

Tree Replacement and Planting New Trees

Section 1.7.2 of our Conditions of Service states:

The Customer shall not build, cause to be built, maintain any structure, or plant any trees, shrubs or landscaping etc., that, in the sole opinion of Thunder Bay Hydro, may affect the safety, reliability, accessibility, or efficiency of Thunder Bay Hydro’s distribution facilities.

Thunder Bay Hydro will not replace trees that have been removed due to poor selection of planting location.

Plant the Right Tree in the Right Place

Learn More

To Ask Questions or Make A Report

To report a concern about trees and power lines, please call Thunder Bay Hydro Power Systems Division at 343-1176.

To request the temporary disconnection of a line from your private residence to the main corridor in order to conduct tree trimming on your private property, call 343-1176.

To report a concern regarding boulevard trees, please contact The City of Thunder Bay, Parks Division at 625-2195.

For more information regarding trees and utilities or tree questions in general, the International Society of Arboriculture webpage provides an excellent source of information on all tree topics.

Tree Trimming Handouts

Our Trimming Brochure can be viewed on screen or printed off on legal sized paper. (PDF) 

Read more about planting the Right Tree in the Right Place