A stormwater treatment device includes a tank defining an internal volume and having an inlet and an outlet, a rotatable screen unit mounted within the tank, the rotatable screen unit being barrel-shaped to define a through path with an inlet end and an outlet end. The rotatable screen unit includes a screen structure with a plurality of screening openings for allowing passage of at least some water from the through path outwardly through the screen structure while inhibiting passage of trash items through the screen structure such that trash items move along the through path from the inlet end to the outlet end. The rotatable screen unit includes a plurality of external drive paddles that rotate with the screen structure and that interact with water that has been screened by passing outwardly through the screen structure interacts with the external drive paddles to cause rotation of the rotatable screen unit.