Alaska's Ice Dam Releases Historic Floodwaters Toward Downstream Residences
Record Flooding Hits Juneau as Mendenhall Lake and River Reach Historic Highs
Mendenhall Lake and the connected Mendenhall River in Juneau, Alaska, are experiencing record high water levels due to a glacial lake outburst flood (GLOF) originating from Suicide Basin within the Mendenhall Glacier. The river crested at approximately 16.65 feet, surpassing the previous 2024 record of 15.99 feet and exceeding the major flood stage threshold of 15 feet.
The water levels peaked around mid-August 2025 and were forecasted to drop throughout the day after peaking around 8 a.m. local time. Officials expected levels to recede to moderate flood stage (below 12 feet) by early afternoon and to minor flood stage (below 10 feet) by late afternoon on the flood crest day.
To prevent and mitigate flood damage, multiple emergency measures have been taken. Authorities have issued flood warnings and urged residents in flood-prone zones to evacuate promptly, emphasizing not to delay in leaving vulnerable areas. Temporary flood barriers and levees have been erected along the river and lake to contain the water, though some seepage around barriers was noted. Power has been cut to parts of the flood zone by Alaska Electric Light & Power (AEL&P) to reduce electrical hazards during flooding. City officials warned residents to avoid flooded roads for safety.
A state disaster declaration was issued by Governor Mike Dunleavy in anticipation of potential catastrophic flooding affecting Juneau neighborhoods. The U.S. Army Corps of Engineers and other agencies are conducting ongoing technical studies and public information sessions aimed at understanding and planning longer-term flood risk reduction for the Mendenhall Valley region given the increasing frequency and severity of these GLOFs caused by glacier retreat and climate change.
As of Tuesday morning, the water level in Mendenhall Lake is already above flood stage at 9.5 feet. Residents are advised to remain updated on flooding information by signing up for emergency alerts. Those who are in evacuation advisory zones will be notified with an evacuation tag on their door. At 17 feet, it is estimated that water will enter the homes around Wildmeadow Lane.
Communities in Alaska have issued flood warnings and evacuations due to the glacial release from Suicide Basin above Mendenhall Lake. Some areas with private property may not have barriers as the city was unable to get unanimous agreement from all those private property owners. In case of a flood warning during the night, the city has planned for schools not to start that day.
Residents should stay away from riverbanks and barriers should conditions worsen. Flooding on the Mendenhall River is forecasted to crest near 16.6 feet by Wednesday, surpassing last year's record level of 15.99 feet. Water levels are expected to go above major flood stage around 9 a.m. Wednesday and to historic levels by the afternoon. At 11 feet, some homes along View Drive will have up to 1.5 feet of water in their yards. At 10 feet, the water will inundate Mendenhall Campground with up to three feet of water covering low-lying areas. At 15 feet, major flooding of homes along View Drive is expected.
Flood barriers have been positioned in "high impact areas" and extended to Diamond Park. Officials are closely coordinating with Juneau schools, which are slated to start school this week. In the 17-foot flood inundation area, residents have been advised to evacuate. A flood hotline staffed by trained volunteers became operational on Monday. The number is (907)-500-0890.
[1] Juneau Empire [2] KTOO Public Media [3] National Weather Service [4] U.S. Army Corps of Engineers [5] Alaska Dispatch News
- In response to the ongoing flooding issue, the National Weather Service is closely monitoring weather patterns and provides regular updates to help manage the crisis.
- As the flooding escalates, residents are encouraged to pay attention to environmental-science reports on the condition of Mendenhall Lake and the Mendenhall River, which could aid in predicting the flood's progression and mitigating potential damage.
