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.
Hello there! This is one of thoses questions that really only you can answer, if you pick a book and a character come back and I will help you with the rest.
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I think it's the third one! definitely not sure tho .. heh