Suicide Basin, an ice-dammed lake on an arm of Mendenhall Glacier, has filled up with meltwater and sent destructive surges of water into Juneau for 3 straight summers.

Residents in some parts of Juneau prepared to evacuate ahead of what could be a record surge of flooding as rainwater and snowmelt in a huge basin dammed by Alaska’s Mendenhall Glacier started to flow downstream toward the capital city.

A rush of glacial floodwater swept down Alaska’s Mendenhall River on Wednesday morning, prompting evacuation warnings in parts of Juneau.