Sentence:  On Big Stone Lake near the headwaters of the <WSD>Red</WSD> River , Robert Dickson , Superintendent of the Western Indian Department of Canada , had a trading post and planned in 1818 to build a fort to be defended by twenty men and two small artillery pieces . 
Meaning of the word marked with <WSD> tags:  a tributary of the Mississippi River that flows eastward from Texas along the southern boundary of Oklahoma and through Louisiana