Scientists with GNWT’s Environment and Climate Change centre say water levels are low across most of the territory but above-average snowpack in the Slave and Liard river basins, combined with a delayed spring melt, could result in near-normal spring flows. Scientists advised weather in the weeks ahead will play a key role in the possibility of flooding.
Data also showed while ice thickness was about average in northern and central areas of the territory, it was “higher than normal” in southern regions. Scientists reported that “colder than normal conditions” in late winter likely led to thicker than normal ice in some regions including Hay River and Yellowknife. According to the report, Yellowknife saw ice thickness levels among highest on record.
Scientists say ice thickness can cause ice jams which increase the risks of flooding.
The findings are part of the spring water outlook report released on Thursday.
Environmental scientists advised that the risk of an ice jam flood is highest during spring break-up.
Some communities were identified as more susceptible to flooding including Hay River and Kátł’odeeche First Nation, Fort Liard, Fort Simpson, Jean Marie River, and Nahanni Butte, Tulita and Fort Good Hope, along with Fort McPherson and Aklavik
“Flood risk across the NWT is expected to be generally near normal but remains highly dependent on spring weather conditions. Rapid warming or heavy rainfall during break-up could increase the risk of ice jam flooding, which is the most common cause of spring flooding in the territory,” read a statement issued by the GNWT.
Environment Minister Jay Macdonald echoed the words of scientists, advising conditions and flooding risks will depend on weather in the coming weeks
“While water levels remain low in many parts of the Northwest Territories, higher-than-normal snowpack in key southern basins could result in near-normal spring flows. Flood risk in the NWT is always closely tied to weather conditions during break-up, and ice jams can occur even in years with lower water levels. ”
To understand spring flow rates scientists monitor real-time water level and flow data, near real-time photographs of water levels and ice from camera footage positioned at water level gauge sites. They also use real-time interpreted satellite imagery of ice conditions, forecasted weather conditions and reports from community flood watch programs.
Spring flows and water levels during break up
GNWT scientists pointed out that it is important to distinguish the difference between spring flows and the water level during break-up. Their report released today provides information about spring flows, the total amount of water that moves through a river during the spring.
Scientists warned that if snowmelt occurs rapidly and water enters rivers quickly, that volume of water would cause water levels to rise higher than if snowmelt was very slow.
“The rapid movement of snowmelt water to a river can also dislodge ice from the riverbank quicker, which increases the chance of strong ice jams. Generally speaking, lower spring flows reduce the potential for flooding, but they do not eliminate the risk. Communities should always prepare for the potential of spring flooding and be aware that water levels can rise quickly in response to ice jams.”
Scientists said the potential and severity for what they call “freshet flooding” will depend mostly on weather conditions over the next weeks and how quickly the snow and ice melt.
A number of factors could influence water levels and the potential for flooding from the rate of snowmelt to the rate of ice melt/break-up to spring precipitation.
These factors interact with current water levels in lakes and rivers, and moisture in wetlands and soil, snowpack volumes (snow water equivalent – SWE), winter temperatures and ice jam locations.
Ice jams: “primary” cause of flooding
Scientists said ice jams are the primary cause of spring flooding in the territory which can result in the back up of large amounts of water. This can cause flooding even when water levels are low.
Low water levels are a trend in the territory observed by scientists, the change in levels became more pronounced in the early 2020s. The GNWT’s Environment and Climate change department defines below average as at or below the 75th to 90th percentile.
“As the spring melt season begins, water levels across the territory, as of April 15, 2026, are generally lower than normal for the main waterbodies across the NWT, with some exceptions for mid-size and smaller rivers,” said the authors of the report.
The data collected for the report showed that summer and fall 2025 were “warmer and drier than normal” across most of the territory, resulting in low water levels.
“These warm and dry conditions have resulted in continued low water levels that have persisted since the late summer of 2022,” said environmental scientists with the GNWT.
According to data collected over the last few months up to mid April, the Great Slave Lake and Great Bear Lake remained at low levels.
average range and historic maximum and minimums (https://www.gov.nt.ca/ecc/sites/ecc/files/resources/2026_nwt_spring_water_outlook.pdf)
Measurements taken along the Mackenzie River indicated that water levels there are also “much lower than normal.”
Scientists said the findings showed that water levels were generally low, but there were some exceptions including the Talston River.
“Notable exceptions to low water levels include the South Nahanni River, Taltson River,
Mountain River and some local rivers in the Great Slave Lake basin such as the Lockhart River and Hoarfrost River.”
The authors of the report pointed out that large river systems like the Mackenzie are mainly driven by upstream basin conditions, while smaller rivers “respond more directly” to local precipitation and snowmelt.
average range and historic maximum and minimums (https://www.gov.nt.ca/ecc/sites/ecc/files/resources/2026_nwt_spring_water_outlook.pdf)
Snowpack accumulation
The report’s data showed snowpack accumulation across the territory from the winter of 2025-2026 was “approximately normal” but there was some variation between regions.
Scientists said that accumulation was “lower than normal” for much of the North Slave Region and also for portions of the Sahtu Region, according to the data.
They found that the opposite was the case for the southern and western regions.
“Snowpack accumulation is higher than normal in the southern and western portions of the territory,” said scientists.
Scientists found that southern areas of the territory and bordering areas of other territories and provinces showed higher snowpack levels.
“Notably, the snowpack is higher than normal for southern basins that lie mostly in northern Alberta, northern British Columbia and the southeastern Yukon. These basins, including the Liard, Hay and Slave River basins, deliver large proportions of water to Great Slave Lake and the Mackenzie River.”
surveys as well as snow survey data from the Government of Alberta.
The Snowpack data was complied from snow surveys conducted in late March. The surveys measure the volume of water produced when a snowpack melts, known as the “snow water equivalent (SWE).”
SWE measures the depth of snow and its density.
Snowpack accumulation was also assessed using a modelled climate application called ERA5-Land. ERA5-Land values to compare the manual measures taken by scientists.
Air Temperatures, Snowmelt Timing and Ice Thickness
Spring weather conditions will influence the timing of snowmelt. Scientists said this will influence the possibility of things like flooding.
“A quick, sudden snowmelt will cause a larger rise in water levels than would a prolonged snowmelt season,” they said.
Factors like ice thickness can influence the chance of ice jams which can lead to flooding.
As environmental scientists pointed out, the chance of ice jams increases as river thickness increases.
“Thicker ice breaks into larger, more resistant pieces that are more likely to accumulate and block flow during spring freshet.”
The thickness of ice is influenced by factors including air temperatures and snow cover. Data from the 2025 to 2026 winter season showed “variable” temperatures across the territory.
Findings showed that ice thickness in southern regions of the territory were “higher than normal” while northern and central areas had about average ice thickness.
Scientists found that “colder than normal conditions” in late winter likely led to ice that is thicker than normal in some regions including Hay River and Yellowknife. Ice in some regions were among the highest recorded.
“In the Town of Hay River and at Fort Liard, CDDF values are higher than normal, suggesting relatively thick ice conditions. Similarly, in Yellowknife, CDDF values rank among the highest on record (following 1967 and 1962), indicating thicker than normal ice,” said the report’s authors.
“In Fort Simpson, Norman Wells and Inuvik, CDDF values are approximately normal but remain higher than in recent years,” they added.
The scientists pointed out the risk of an ice jam flood is highest during spring break-up.
“The primary driver of ice jam occurrence is weather conditions immediately before breakup and during break-up. Rapid warming and heavy rain can trigger “mechanical” break-ups (higher risk), while gradual warming can encourage a thermal decay of the ice in place (lower risk).”
Other conditions such as snowfall and winter air temperatures also play a role in the potential for ice jams. When water levels are high the risk is greater.
“The potential severity of flooding, if an ice jam occurs, increases when water levels are already high, when snowpacks are large, and when river ice is thick.”
Outlook by region
In the North Slave and Tłįchǫ Regions, snow surveys showed that the snowpack in the Yellowknife River basin was approximately normal at 98 per cent of normal.
Snowpack measures in the Snare River basin were lower than normal at 77 per cent of normal as of early April 2026.
The snowpack at other North Slave and Tłįchǫ sites is approximately normal at 91 per cent of normal.
“A lower than normal to approximately normal snowpack in the North Slave and Tłįchǫ Regions will still contribute some moisture to recharge the. However, water levels on most local lakes and rivers are not expected to be significantly higher than in 2025, unless rainfall this summer is at or above normal levels,” said the authors of the report.
Snow surveys showed that the snowpack in the South Slave Region was higher than normal at 113 per cent of normal.
“SWE values are higher than normal in the headwaters of the Peace River and exceed 200% of normal in the midreaches of the Peace and Athabasca rivers. Basin-averaged percent of normal for Slave River basin SWE is much higher than normal.”
Scientists predicted the Great Slave Lake will receive a much higher than normal snowmelt input this spring. They said increases in water levels will also depend on spring and summer rainfall.
Data showed water level on Great Slave Lake has been very low (less than the 5th percentile) for the past three summers since 2023. The three years were the lowest on record, said scientists.
“Great Slave Lake water level is currently 17 cm lower than this time in 2025 and 16 cm higher than this time in 2024.”
The water levels and flow rates on the Slave River have ranged from lower than normal to much lower than normal since December 2025.
Scientists also reported that water levels on the Peace River are variable depending on the location along the river, where levels are higher than normal at the Town of Peace River and much lower than normal downstream at Peace Point.
“This variability is likely reflecting a delayed response to upstream variations in outflows from the Bennett Dam. Water levels on the Athabasca River are similarly higher than normal near the headwaters and lower than normal further downstream near Fort McMurray.”
The water levels on Lake Athabasca showed lower than normal measures.
Snow surveys show that snowpack in the Taltson and Tazin River basins were higher than normal at 118 per cent of normal. Water levels on the Taltson and Tazin rivers were approximately normal.
“The Taltson and Tazin river basins recovered from low water levels in 2023 and have since been an exception to widespread hydrological drought in the territory,” said scientists.
Snow surveys showed that the snowpack in the Hay River basin is higher than normal this year at 119 per cent of normal.
Data from neighboring jurisdictions showed the snowpack SWE in the upper Liard basin is much higher than normal at 142 per cent of normal.
Further downstream, snow surveys showed SWE values are higher than normal at 118 per cent of normal
Snow survey data in the lower Liard basin in the NWT showed “higher than normal” SWE values at 129 per cent of normal. Snow surveys in the other areas of the Dehcho Region showed snowpack was higher than normal at 115 per cent of normal.
Liard River water levels showed measures lower than normal with the basin not having seen any significant spring snowmelt inputs.
The water level on the Mackenzie River at Fort Simpson showed measures currently “much lower than normal.”
In the Sahtu Region, snow surveys show that snowpack SWE values are approximately normal at 104 per cent of normal.
Great Bear Lake water levels were at their lowest level on record for this time of year and Great Bear River is also at its lowest level on record.
Snow survey data for the Peel River basin showed that the snowpack is higher than normal at 118 per cent of normal. Snow surveys in the Inuvik Region showed that snowpack is also higher than normal at 125 per cent of normal.
More detailed information is available in the report. The report also includes average air temperature measures for each region of the N.W.T. going back to 1950.
