It's Not a Lake is one of the Collectables found in the Alan Wake 2 New Game Plus mode "The Final Draft." It is one of the pages of the Return manuscript.
Transcript[]
The surface of a lake was a black mirror. The upside-down reflection identical, yet darker. A window into a darker world than ours. A doorway. A hush so profound, it rang like a scream. As if the last echo of the terror had just died. Inside the steep cliffs of the caldera, everything echoed. An echo chamber. Like a fractured skull.
A shadow fell on Cauldron Lake. Something of impossible scale loomed over it, blocking the sky. Ahti, the janitor, leaned close. Took a hold of the rim of the crater. Lifted up his janitor's bucket. The water sloshed. Swirled inside like a vortex. Gently humming a tango, he poured the water on the attic floor.
Location[]
After the point of no return, in Cauldron Lake - on the ground in the pathway after crossing the bridge and just before jumping down to the beach to join the Old Gods.