Sruth in Aghaidh an Aird also flows out to the northern shore, just west of the Glencar Waterfall outflow.

The lake drains west into the Drumcliff River, which in turn flows into Sligo Bay.

[7][n 1] The ecology of Glencar Lough, and other Irish waterways, remain threatened by curly waterweed, zebra mussel, and freshwater clam invasive species.

[13] The Glencar Water Company has its bottling plant located near the lake's northern shore.

The company, established in 2008, sells water drawn from an onsite spring emanating from within the nearby Dartry Mountains.