I scan over the descriptions to check for irregularities or significant identifiers. So your yellow lake would be noteworthy to me or if a person is described with long hair. I don't mentally imagine a long hair person, but I try to remember it, so if later somebody sees a long haired person in the distance I know which character is referenced.

And yes if I don't recognise anything noteworthy, I don't make a mental note, it's just a normal lake, nothing important to remember.

But that isn't always working out for me. In Neverwhere the Marquis de Carabas is described as being pitch black. Which I fully didn't get and so was wondering why all the fan art made him so black that you can't recognise features. Because that was how he was described and I missed that important fact.