Sentence:  But it had , as was usual in southern cities of this sort , a Black Bottom , a low region near the <WSD>river</WSD> where the Negroes lived - servants and laborers huddled together in a region with no sewage save the river , where streets and sidewalks were neglected and where there was much poverty and crime . 
Meaning of the word marked with <WSD> tags:  a large natural stream of water (larger than a creek)