Nooksack Dace are a small (<10.5 cm) streamlined fish, with a sub-terminal mouth (the snout overhangs the mouth), sometimes with a black stripe in front of the eyes. Scales are small with pale markings visible at the back and front of the dorsal fin when viewed from above. The tail is forked. The rounded back is olive-grey; the belly is silvery-white with a dull brassy stripe along the sides. Lower sides often splashed with dusky speckles. Sexes are alike, but males tend to have longer and darker pectoral fins. Juveniles have a very conspicuous black line on their sides, from snout to base of tail.