Chu Tsän Dek (Engineer Creek in Hän) near the Dempster Highway, September 2025.
This blog post is written with the collaboration of Al von Finster (retired from the Department of Fisheries and Oceans), Sean Carey (McMaster University), Elliott Skierszkan (Carleton University), and Brian Horton (YukonU).
It is well known that climate change is generally causing a rise in air and water temperatures over time. Warming streams alone represent a concern for aquatic life as most fish species can only thrive and spawn in a relatively narrow temperature range. However, could climate change drastically but indirectly alter other water quality parameters such as metals concentration, pH or Dissolved Oxygen?
Recent scientific papers have documented that dozens of creeks have turned orange in Alaska (here and here) as a result of warming air temperatures, with impacts that are summarized in recent articles (here, here and here). These changes are cause for significant concerns about altered water quality and aquatic habitats. There is no industrial activity in these watersheds, nor is there any mining exploration or exploitation. The chemical processes leading to a transition from clear water and clean gravel riverbeds to milky or orange water flowing over rusty sludge deposits are not exactly simple, and they may vary between watersheds (e.g., the presence of wetlands) and over time. The publications from Alaska have indicated that, in most cases, groundwater is flowing in new pathways that are opening as permafrost thaws. Water that once flowed in a stable active layer now flows against and within formerly frozen geologic units that contain sulphide minerals (e.g. pyrite). Sulphide minerals are unstable in the presence of oxygen and water, and break down to release acidity, metals (e.g., iron), and sulphate. When groundwater enters streams, acidic (low pH) water, combined with bacterial activity, probably explain the orange, slimy deposits on the channels bed. See diagram below for a simplified side-view of the process.
Schematic cross-section of a riparian zone before and after permafrost thaw explaining why some creeks are turning orange.
Based on observations over recent years, it appears that the Yukon is not spared from this phenomenon. Creeks are becoming “rusty” on our side of the border too as the North warms. Red Creek, located at Km 168 of the Dempster Highway, is probably named because its rusty flow has been evident for some time. Our team travels regularly to Chu Tsän Dek (Engineer Creek in Hän) for a project about riverbank erosion and flood risk mitigation. The creek, with its striking colour, as shown in the first picture above, can be observed from multiple points between Km 165 and 195 of the Dempster Highway. It is also possible to see acidic water emerging from the ground near the highway (see picture below). Al von Finster, retired habitat biologist Fisheries and Oceans Canada, revealed to our team that the water in the Chu Tsän Dek was relatively transparent until the end of the 1970s.
Acidic water ponding near the Dempster Highway in April 2024 (with its typical sulfur smell).
It has been observed in recent years that the flow of the East Blackstone (picture below), feeding into the Tthʼoh zrąy dëk (Blackstone River in Hän, Tth’oh zraii njik in Gwich’in), then into the Peel River watershed and the water carried by the upper North Klondike River, tributary of the Tr’ondëk (Klondike River in Hän) have recently turned milky, with orange deposits on the channel bed that appear to significantly modify the aquatic habitat. This slime contains air bubbles that resemble hundreds of aquatic eyes staring at us as we walk in the formerly pristine, braided section of the river in Tombstone Territorial Park.
East Blackstone River in the Tombstone Territorial Park in August 2025. Orange deposits are mainly visible in slow flowing, shallow areas.
The Gwazhàl Njik (Ogilvie River in Gwich’in) below Chu Tsän Dek also seemed to be more turbid during our latest field trip in September 2025 than in former years. Back in 2020, sediment bars along this river were composed of stones with a wide range of colours, from light yellow to dark red and black. Now, the gravel is stained in dark orange (picture below), even well above low flow levels, which indicates that the water can be rusty at high flow too. In other words, several creeks and rivers in the Ogilvie Mountains are apparently changing fast, just like what has been reported in the Brooks Range in Alaska.
Gwazhàl Njik (Ogilvie River in Gwich’in) as seen from the Dempster Highway in September 2025. The perimeter of the gravel bar on the far side of the river is stained in orange.
Since permafrost is now irremediably thawing and groundwater flow paths are changing as a result, it is possible that this rusting process will not be ephemeral in most affected creeks and watersheds (e.g., the Chu Tsän Dek has been orange for decades). If it became increasingly common, just like in the Brooks Range, the rusting of northern creeks could represent one of the most consequential climate change-driven hydrological processes of the century.
Researchers are working to better understand the conditions of creeks located in Central Yukon. McMaster University and Carleton University are currently documenting water quality in several small and large streams that cross or flow along the Dempster Highway and have submitted a paper for peer review on this topic.
It is too early to confirm at what level, from an ecological perspective, these creeks, the rivers they feed into, and the surrounding wilderness will be affected by this rather drastic change in water quality. Here are some research questions that need to be answered through a collaborative effort, which must involve First Nations that are deeply affected, at multiple levels, by climate change:
- Based on a geological and permafrost assessment, can we identify the creeks that are likely to become orange in the future?
- Beyond climate trends, what is the impact of year-to-year and seasonal weather on the toxicity of orange creeks?
- Considering food chains and cumulative impacts, should we expect a decline in biodiversity in valleys where creeks are becoming orange as well as in downstream environment?
- How much suitable Salmon, Dolly Varden, Arctic Char, etc. habitat will remain for spawning (and overwintering habitat) along and downstream of acidic water effluents? Can this process end up affecting coastal habitats as well?
- Can this acidity kill riparian vegetation (e.g., willows) and, consequently, promote a destabilization of creek channels through increased erosion rates?
- What is the impact of rusty streams on the life expectancy of drainage infrastructure, more specifically on metal culverts?
Back in 2019, an agreement was signed to protect the Peel watershed. It is unfortunate that some of its creeks and rivers are now becoming polluted indirectly because of human activity. Can something be done to reverse or improve the situation? Solutions to this challenge are not immediately apparent. It is probably unreasonable to consider treating the water that emerges from the ground, sometimes at multiple points, before it enters the environment. Similarly, there aren’t obvious ways to cool permafrost at a large scale. Compacting the snowpack every winter near acidic effluents could potentially promote heat loss and freeze the ground deeper at a small scale, but this would be impractical over large areas. However, it can be presumed that considerably reducing our greenhouse gas emissions as soon as possible could limit future warming and reduce the rusting of additional headwater creeks further north.