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Taking Care of the Water Supply Areas


Our watersheds cover about 60,000 hectares (150 times the size of Stanley Park) of protected land secured under a 999-year lease from the Province. Most of this is Crown land, with some sections owned by the Greater Vancouver Water District. The primary purpose of our watersheds is to produce high-quality drinking water​. They are protected from human access, urban development, and human-caused disturbances to keep our water clean.

By protecting these watersheds for drinking water we are also protecting a lot of forested land.

Western hemlock looper outbreak

An outbreak of western hemlock looper moths impacted Metro Vancouver’s Capilano, Seymour, and Coquitlam watersheds, Lynn Headwaters Regional Park, and the North Shore from 2018 to 2021, resulting in tree defoliation and mortality.​

The western hemlock looper is a native species that is an important part of the natural coastal forest ecosystem, as looper larvae (caterpillars) feed on trees and understory vegetation that grow in the Lower Mainland. 

Western Hemlock Looper
Western Hemlock Looper



How long did the outbreak last?How long did the outbreak last?<div class="ExternalClass14AEB716A3F4495A97C79603CEC6F247"><p>Outbreaks can typically last three to four years; this last outbreak lasted four years. Outbreaks are not uncommon and populations build every 11 to 15 years in our region. The extent and duration of outbreaks depend on weather and other environmental factors.<br></p></div>
What role does climate change play in forest pest outbreaks?What role does climate change play in forest pest outbreaks?<div class="ExternalClass848DE193D44A48DBBF84D5EEC5F7ABC8"><p>It is expected that climate change - longer, drier summers in particular - may contribute to more frequent and intense pest outbreaks as forests adapt to a changing climate. Metro Vancouver continues to intensively monitor climate factors which may impact the forests upon which we all rely.​<span id="ms-rterangecursor-start"></span><span id="ms-rterangecursor-end"></span><br></p></div>
Which trees are being damaged?Which trees are being damaged?<div class="ExternalClass322FB0557B6C4CFDB54FA5BE43B06C0A"><p>The looper prefers western hemlock trees, but also feeds on other locally occurring conifers including Douglas-fir, amabilis fir and Sitka spruce. Bigleaf maple, red alder and forest understory vegetation may also be hosts to feeding caterpillars when populations are high.</p>​<br></div>
Did some trees die?Did some trees die?<div class="ExternalClass223EC0BE2B794F57A37FC0D0EDE26490"><p>Some trees were less tolerant of being defoliated – western hemlock in particular – and succumbed to the damage. Tree mortality is most noticeable in the Capilano Watershed, where more than 400 hectares experienced some degree of mortality.<br></p></div>
Are the dead trees a hazard?Are the dead trees a hazard?<div class="ExternalClass96B13358C066403788F369F16F568EBC"><p>Trees are typically not an immediate hazard to surrounding property following death. It typically requires years of decay before trees become structurally weaker. Trees near property are monitored by certified hazard tree assessors and will be removed when there may be a hazard present. </p>​<span id="ms-rterangecursor-start"></span><span id="ms-rterangecursor-end"></span><br></div>
What is the impact to forest health?What is the impact to forest health?<div class="ExternalClassC92D117649B44FE3807D5D7BCB58B76F"><p>Outbreaks like this are an important component of ecosystem dynamics and essential in recharging the ecosystem. These outbreaks allow younger trees to emerge, while supporting nutrient recycling. This is a natural and important process.​<span id="ms-rterangecursor-start"></span><span id="ms-rterangecursor-end"></span><br></p></div>
Will there be an increase in wildfire risk as a result of the tree mortality?Will there be an increase in wildfire risk as a result of the tree mortality?<div class="ExternalClassD47D851B7FDE431DA541251713866F57"><p>Although the appearance of dead and dying trees can be worrisome, overall fire risk is not greatly increased. As trees decay, they add to the nutrient load and encourage new understory growth within a short time. ​</p>​<br></div>
Will dead trees on a steep slope result in instability issues?Will dead trees on a steep slope result in instability issues?<div class="ExternalClass8790CAA39236453BBC0114B377419FE4"><p>This will depend on geotechnical factors and the severity of tree mortality. As the trees were generally healthy prior to dying, the root systems and especially the main structural roots will take a long time to decay, therefore providing stability for many years while new native vegetation and trees establish.<br></p><p>A geotechnical specialist will make recommendations to determine the risk associated with significant tree loss on slopes with potential for stability and erosion issues.</p>​<span id="ms-rterangecursor-start"></span><span id="ms-rterangecursor-end"></span><br></div>
Will there be impacts to drinking water quality?Will there be impacts to drinking water quality?<div class="ExternalClassC2539AC033CA469E895E4CAE2296677C"><p>Metro Vancouver does not expect any impacts to our drinking water from this outbreak. Source water from areas most heavily impacted on the North Shore is filtered and slope stability will be closely monitored.</p>​<span id="ms-rterangecursor-start"></span><span id="ms-rterangecursor-end"></span><br></div>
Will Metro Vancouver be spraying chemicals or other treatments to control this outbreak in the drinking water supply areas?Will Metro Vancouver be spraying chemicals or other treatments to control this outbreak in the drinking water supply areas?<div class="ExternalClass099A85493EDF4F858B747C6BF408F674"><p>No. With no impacts to water quality anticipated during this short-term outbreak, spraying is not considered required mitigation. Metro Vancouver does not support the use of pesticides within the watersheds. Although the forest industry and provincial programs commonly use aerial biological spray products for pest control, partly to maintain timber value, Metro Vancouver is using a minimal intervention approach coupled with intensive monitoring to detect any water quality issues or other environmental concerns. </p>​<span id="ms-rterangecursor-start"></span><span id="ms-rterangecursor-end"></span><br></div>

Erosion control

Erosion is where soil and sediment is worn away by wind, rain or even glaciers. In watersheds, steep banks combined with severe weather can result in landslides or creeks and rivers banks flooding. Tiny particles in our water supply add to the challenge of cleaning our water.

To minimize this risk, Metro Vancouver deactivates old roads, stabilizes slopes, strengths creek beds, and re-vegetates disturbed areas.

Water monitoring and forecasting

Monitoring stations throughout the watersheds help predict the impact of weather patterns on water quality. For example, in-stream data collection can signal when erosion in a tributary (side stream) may reach the reservoir.

Long-term data on precipitation and snowpack is also is useful for examining trends affecting water supply in our region, including the impacts of climate change.

Maintaining ecosystem health

These huge areas of forested land and protected wildlife habitat are valuable natural assets to our region. The ecological health of our watersheds contributes significantly to the quality of water, soil, and air we enjoy in this part of the world.

Our watersheds are covered with old-growth and second-growth stands of predominately western red cedar, Douglas-fir, Sitka spruce, and hemlock trees. They are also home to wildlife such as the Douglas squirrel, barred owl, black tailed deer, and black bear.


Fish are present in all of the rivers flowing from our watersheds. While our first priority is to provide high-quality drinking water, healthy fish habitat and populations play a key role in a balanced ecosystem. Metro Vancouver works on initiatives to restore habitat, and replenish fish stocks in the watersheds including protecting and creating healthy habitat to live, rear, and spawn; maintaining minimum populations; and providing safe passage past the dams. Salmon are a special consideration not only for ecosystem health but also for their cultural significance.​​​​



Capilano Salmon Catch and ReleaseCapilano Salmon Catch and Release562019687

Minimal ​intervention

When natural disturbances such as plant disease, fire, or wind damage occurs, Metro Vancouver takes a minimal intervention approach. Unless there is a risk to public safety or water quality, these natural processes are allowed to take place.​​



Fire Protection in the WatershedsFire Protection in the Watersheds539337837

Public engagement

Another key part of maintaining a sustainable and resilient water supply, is to provide opportunities for citizen engagement. School and public programs offer learning tools and guided field experiences to help people connect these places to their daily lives. Education initiatives create trust and confidence in our public water supply and allow for opportunities to share ideas; part of Metro Vancouver’s approach to promoting the sustainable use of water.

The Lower Seymour Conservation Reserve (LSCR) is located below the dam in the Seymour Watershed. It is an area of land that does not drain directly into the reservoir and is therefore open to the public. Visitors can explore the area through a number of recreational and educational opportunities.

River levels

Metro Vancouver provides recent and current river levels and flows of the Capilano and Seymour Rivers. This information may be of interest for recreation purposes.​​​​



Seymour River Fish TrappingSeymour River Fish Trapping219040785

 Related links



Reservoir Levels and Water Use, Reservoir Levels & Water UseReservoir Levels and Water Use
Take a Tour of the Watersheds, Take a Tour of the WatershedsTake a Tour of the Watersheds
Watersheds & Reservoirs, Watersheds & ReservoirsWatersheds & Reservoirs

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