Geologists predict that when the two lakes merge, Alsek River will abandon its current outlet in favour of the steeper way to the ocean through Grand Plateau Lake and a small embankment, moving its outlet some 17 miles (27 km) to the southeast, within the confines of Glacier Bay National Park.

After flowing south into the northwestern tip of British Columbia, it is joined by the Tatshenshini River in Tatshenshini-Alsek Park.

Although the river is navigable by kayak or rubber raft in its northern reaches, it rapidly becomes unnavigable—for any but the most experienced and skilled kayakers—at Turnback Canyon.

The last such blockage took place in 1850; its release created a massive flood, washing away everything in its path on the way to the Pacific.

Despite this sincere warning from a man who apparently felt lucky to be alive, groups of expert kayakers have successfully run Turnback Canyon since then.

Chum and pink salmon can also be caught, but are not generally sought after due to their relative lack of worth/quality.

The area also supports subsistence and sport fishing, as well as multiple sight-seeing, hunting, and animal watching lodges.