Each summer in the mountains above Juneau, Alaska, meltwater from the massive Mendenhall Glacier flows into mountain lakes and into the Mendenhall River, which runs through town.

One of Alaska's most populated cities is bracing for potentially catastrophic flooding as a basin dammed within the Mendenhall Glacier has started to release water.

Update, 6:25 a.m. Wednesday: The Mendenhall River hit a record level as of 6 a.m., according to the National Weather Service. The river is in major flood stage at 16.17 feet and rising, the agency said. That surpasses the record set last year of 15.99 feet.