Secret Pathway + Secret lake??

While i was watching Happy77's new video today about the map , i noticed something different. A pathway and a lake! Take a look

Did you notice it? If not , take a look at the image below , its more clear!

This is exiting! That lake , is what probably fed the forest's stream in the medieval party! 

What do you think? Do you think it could become a new room?Tell us in a comment!