Complex sentence: Crossing the Back Rivers by a series of bridges is the Northern Outfall Sewer which feeds the Abbey Mill Pumping Station, both of which were designed by Joseph Bazalgette in the 1860s.
Split into simpler sentences: Crossing the Back Rivers by a series of bridges is the Northern Outfall Sewer. It and Abbey Mill Pumping Station were, both designed by Joseph Bazalgette in the 1860s.