Sentence:  Into the <WSD>fever swamps</WSD>, they marched us . . . And they set us to work draining the swampland and toiling in the sun . . . . . . They set us to toiling . . . They took the white fleece of the cotton and the sweetness of the sugarcane and made them bitter and bloody with our toil . . . 
Meaning of the word marked with <WSD> tags:  An area of stagnant water and hot temperatures that acts as a breeding ground for disease vectors such as mosquitos.