The sand roller Percopsis transmontana is endemic to the Columbia River drainage and has been collected from western Idaho, southern Washington, and northern and western Oregon. In Oregon, the sand roller has been collected from the Columbia River, the Willamette River and several of its tributaries. In 2005, the Native Fish Investigations Project surveyed historical locations in the Willamette River basin to determine the status and current distribution of sand rollers. Sand rollers were found at 41% of the locations sampled, including collections from most Willamette River subbasins. Sand rollers preferred slow water habitats in low gradient streams and were most frequently associated with roots, other large wood, and undercut banks over sand or gravel substrates. Sand rollers were more common at locations containing only native fishes; larger numbers were collected at locations where nonnative fish were absent. Infrequent reporting of this species is probably related to secretive daily behavior and gear inefficiencies, rather than to actual rarity.

The sand roller is a small perch-like fish with spiny rays and speckles on the sides and fins. This is a small species, rarely reaching 10 cm long. Sand rollers have blue-green coloration, coarse (ctenoid) scales, and an incomplete lateral line. An unusual feature of this fish is that it has an adipose fin. Males tend to be smaller and more slender than the females.

These fish are active nocturnally and are most often found in pool margins of low gradient reaches of small to large rivers. They are found around submerged roots, complex woody debris and brush, and undercut banks over sandy or rocky substrates. They are also found near vegetation over sand. During the day, they have been found in pools up to four meters deep in small depressions over sandy substrates. In deep rivers, observations indicate that sand rollers may exhibit diel periodicity, moving into deep waters as cover during the day and into shallow waters at night.

Sand roller spawning commences in the spring and continues through mid-summer. Sand rollers have small (0.14-0.17 mm diameter) adhesive eggs and are thought to spawn on gravel or other rocky substrates. Egg numbers range between approximately 1,100 and 3,400 for females 76 to 91 mm. Sand rollers in the Columbia River mature beginning at age 2; all were mature at age 3. They feed principally on aquatic insect larvae (Diptera and Trichoptera) and crustacean zooplankton.