The smallmouth bass averages about 12 inches in length. It is green-brown or yellow-brown on the back and sides. The belly is white with dusky pigment. There are faint, dark bars on the sides and stripes on the cheek. The small, short, first dorsal fin is joined to the taller, second dorsal ﬁn. The end of the upper jaw does not extend behind the eye. The tail fin of the smallmouth bass young has three colors: white on the tip; black in the center; and yellow at the base.
The smallmouth bass may be found statewide in Illinois but is much more common in the northern one-half of the state. Siltation, ﬂuctuating water levels and poor water quality have led to its decline in many parts of Illinois. This ﬁsh lives in clear, gravel- or rock-bottomed rivers with moderate to fast current that remain relatively cool throughout the summer. It is intolerant of silt and turbidity. Spawning occurs in May or June over nests excavated in gravel. From 2,000 to several thousand eggs are guarded by the male who continues to stay with the fry for a day or two after hatching. Hatching is dependent on water temperature and may take as little as two or three days. Young smallmouth bass reach maturity in three to four years. This ﬁsh eats crustaceans, insects and other ﬁshes. It will hunt on its own but sometimes follows turtles or suckers as they feed along the bottom, catching insects that they dislodge and do not catch.