The Mississippi River is a tributary of the Ottawa River in Eastern Ontario, Canada which has no relation with the Mississippi River in the United States. It is 200 kilometres in length from its source at Mackavoy Lake, has a drainage area of 4,450 square kilometres, and has a mean discharge of 40 cubic metres per second. There are more than 250 lakes in the w…The Mississippi River is a tributary of the Ottawa River in Eastern Ontario, Canada which has no relation with the Mississippi River in the United States. It is 200 kilometres in length from its source at Mackavoy Lake, has a drainage area of 4,450 square kilometres, and has a mean discharge of 40 cubic metres per second. There are more than 250 lakes in the watershed.