The Lake of Hali is ahe cloud-lake near the city of Carcosa, in the Hyades. Hastur is said to be "the Sleeper beneath the lake." When the Spawn of Cthulhu wake and thrash about in the lake it is called "the Time of the Frothing". Mists and cloud banks commonly cover the surface of the lake (or else the whole lake is made of mist?), and the ghostly presence of Carcosa can sometimes be seen. There are several lakes in the area, and one text refers to "the black lakes of Hali", however the other lakes have their own names (such as Dehme) Called "The Lake of Hali" as well as just "Lake Hali" and is sometimes termed "the Black Lake."
It is connected with the Hastur Myth Cycle.
The Lake of Hali was added to the Mythos by H. P. Lovecraft, based on coinage by Ambrose Bierce and Robert W. Chambers; it has been greatly and conflictingly expanded upon since.