A deep and permanent natural high-mountain lake, it is located in the heart of the eastern High Atlas. Together with Lake Tislit and Lake Ifni on the Toubkal, it constitutes the highest lakes in North Africa (2270 m for Isly and 2225 m for Tislit). In addition to their morpho-hydrological originality, their biological value lies in the presence of an endemic form of brown trout.

As a permanent water reservoir, this lake contributes significantly to the recharge of the groundwater table. In addition, the site is very famous as a tourist pilgrimage site, in particular thanks to the Imilchil festival, known as Moussem of the Betrothal, which has acquired international fame.