It flows to the south of the Eugenisee hydroelectric reservoir but does not normally feed into it; the inflow from the Erlenbach and down from Trüebsee via the power station is usually enough to maintain required levels.

After Örtigen on the outskirts of Engelberg the river turns northwards and starts to descend a steep gorge, the Aaschlucht (possibly named as a play on words referring to the Aareschlucht).

Here a hiking trail, the Erlebnisweg Aaschlucht (the "Aa Gorge Discovery Way") follows the river, crossing over it via a total of eleven foot and suspension bridges.

There is a dammed channel feeding a power station at Hostetten, and soon after that the river turns eastwards and crosses under the A2 autobahn.

Finally the river flows through the town of Buochs and enters Lake Lucerne alongside the Aawasseregg beach (435 m (1,427 ft)).