Bacteria can cause a foul odor in the genital area.
In women the condition is known as bacterial vaginosis which is an overgrowth of the normally occurring bacteria that causes the foul odor or fishy smell in the Vaginal area.
If you're a male you could have bacterial growth down there as well and need to use some antibacterial soap or some apple cider vinegar to help get rid of the bacteria growing down in your genital area.
You can soak in a warm bath and add a cup or two of apple cider vinegar to the warm bath water which can help kill the bacteria in both woman and men.
Soak in the warm bath with apple cider vinegar for at least 30 minutes so that the bacteria is killed off.
You may need to do this for a week or two to fully get rid of the bacteria in the genital area.
You can also get some cream from your doctor for treating the bacteria in the vaginal area or genital area.