Maroon-colored stools or bright red blood usually suggests that the blood is coming from the lower part of the GI tract (large bowel, rectum, or anus). Hemorrhoids and diverticulosis (an abnormal pouch in the colon) are the most common causes of lower GI bleeding. Abnormal collections of blood vessels called arteriovenous malformations (AVMs) and tumors in the intestine may also cause lower GI bleeding. However, sometimes massive or rapid bleeding in the stomach causes bright red stools. Consult a Gastroenterologist.