Kennicott River rising after Hidden Creek Lake drains; crest expected Monday

The Kennicott River outside McCarthy is rising after Hidden Creek Lake began dropping Saturday, July 18, and NWS Anchorage expects the river to crest by Monday evening.

Wrangell–St. Elias National Park and Preserve rangers confirmed Sunday that they observed significant new water releases next to the Kennicott Glacier flowing into the river. NWS Anchorage issued a Hydrologic Outlook for the McCarthy area, warning that water levels will continue rising over the next 24 to 48 hours. The river is forecast to stay below minor flood stage, and widespread flooding is not anticipated, but the outlook warns of rapid water level rises measured in feet per day, bank erosion from fast-moving water undercutting riverbanks, and large debris including trees carried downstream.

The hazards don't stop at McCarthy. The NPS advisory notes that dangerous conditions extend downstream to the Chitina and Copper Rivers, putting boaters and subsistence fishermen along those corridors at risk as well.

What's happening is a jökulhlaup, an Icelandic term for a glacial lake outburst flood. Hidden Creek Lake sits dammed by Kennicott Glacier and drains subglacially each summer when water pressure punches through the ice. NPS described the event as an annual high-water occurrence, with the lake beginning to fall July 18 before rangers observed significant releases the following morning. Research published in the Annals of Glaciology documented peak discharges from these events reaching up to 1,300 cubic meters per second. Local outfitters who run the Kennicott describe it as an event they plan around each summer.

NWS Anchorage advises recreationalists, hikers, and packrafters in the McCarthy area and along the Kennicott River to use extreme caution, avoid parking vehicles and camping near the immediate riverbanks, and not attempt to cross fast-flowing water. Real-time river level data is available through the USGS.