Starting in C Locrian and switching to C Phrygian was a smart way to create that mysterious shift, and the drone note change in the first 30 seconds works well as a structural device. My main note is that the track drifts out of ambient territory in places, so pulling back some of the foregrounded elements would help it sit more firmly in the genre. The lake theme comes through well, especially given how much thought you put into the setting.
Really solid work; I really like the compositional elements!
