This is the 1736th most frequent Spanish word.
fondo
"Fondo" means "bottom," "background," "fund," or "depth," depending on context.
In this sentence, 'fondo' is used to mean the 'bottom' or the deepest part of something, specifically the lake.
El fondo del lago es muy profundo.
The bottom of the lake is very deep.
Here, 'fondo' refers to a 'fund', indicating a reserve or collection of resources, in this case, financial savings.
Tengo dinero guardado en mi fondo de ahorro.
I have money saved in my savings fund.
In this usage, 'fondo' stands for the 'back' or furthest part of a space, in this context, the room.