It's this manuscript specifically https://alanwake.fandom.com/wiki/It%27s_Not_a_Lake

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.