Complex sentence: The Rhine, for example, through which "Moby Dick" swam at the time, was justifiably characterized as a sewer, since waste water from cities and chemical plants was for the most part poured in unfiltered.
Split into simpler sentences: The Rhine, for example, through which "Moby Dick" swam at the time was charactized with thorough justification as a sewer. Waste water from cities and chemical plants was for the most part poured in unfiltered.