The heatwave, with temperatures of nearly 50C (122F), is believed to have killed hundreds of people since last week in western Canada, along with the US states of Oregon and Washington.
The extreme heatwave is caused by a “heat dome” of high pressure over the region, which is being made more intense by the human-driven climate crisis.
University of Washington assistant research professor of glaciers and climate TJ Fudge told the state’s Komo News the extreme conditions were also causing the biggest glacier melt in the state in about 100 years.
Snow and ice on Washington’s iconic Mount Rainier– the most glaciated peak in the contiguous USA – is likewise melting.
Scott Pattee, of the Washington Snow Survey and Water Supply Forecasting, said: “Now we’re melting into glaciers and so probably that is what’s causing the milky waters down below.
“It is a big deal, I mean we’ve been losing glaciers a lot lately due to climate change or whatever it is - but to have them go this rapidly is really quite scary.”
Mr Pattee said Paradise, an area on the western slope of Mt Rainier, lost nearly 3ft of snow in just five days.
The melting, which comes months after heavy winter snow, raises the risk of fires by exposing surface vegetation, experts say.
“In my 30 years here in Washington doing this job, I don’t recall ever seeing this rapid of a melt when we have a lot of snow,” Mr Pattee told Kiro7.
“I’ve seen this amount of snow when we’ve had low pack years. But when we have this much snow? No. I think this is definitely unprecedented. We’re going to set a lot of records.”
Authorities in British Columbia recorded at least 486 “sudden and unexpected” deaths between Saturday and Wednesday.
Another 60 fatalities in Oregon have been linked to the heat and more than a dozen in Washington.