Generally speaking, that is correct. A dystopia is the opposite of a utopia, and is a place which we define as unpleasant or bad. Therefore, what you might find in a dystopia is what you would consider as being unpleasant or bad. Hence, if you think polluted lakes and rivers are unpleasant, then they are likely to be part of a dystopia "for you". However, each person's dystopia may be different, as it depends on personal preference, or in this case, personal disgust.
Core. It sounds the same, but it is a completely different word.
Its a metaphor :) the kids room is being compared to the disaster area to make the point that it is messy
