Complex sentence: Unlike the Hackney Brook further south, the Moselle is not a lost river-though long stretches of it have been culverted, it does not disappear into the London sewer system, and much of its route can be easily traced.
Split into simpler sentences: Unlike the Hackney Brook further south, the Moselle is not a lost river. Although long stretches have been culverted, it does not disappear into the London sewer system, and much of its route can be easily traced.