The code should be on a collision response function, for example using the signal "area_entered" on Area2D2. Then you need to place the LakeView so it moves with the camera. In 2D I think you can just make it a child of Camera2DPlayer. Then, in "area_entered" find the LakeView node and set visible to true (you can set visible false on "area_exited"). To find the node, you just traverse the scene hierarchy like it were a folder tree in your operating system.
So it could be something like this (depending on your tree). Place this near to top of the Area2D2 code (before any function):
onready var lake_view = get_node("/root/Root/Player/Camera2DPlayer/Container/LakeView")
Then on the signal callback, do this to show the lake image:
lake_view.visible = true
You'll also need to set the visible property of the LakeView to false so it is invisible when starting.
Hope that helps.