A screening installation includes, provided in a flume (5) conveying a fluid flowing with a total flow QE: a screening device (10) including a screen which includes at least one filter member in order to screen a fraction Q10 of the total flow, at least one first passage (31) in the flume which is adapted to allow a fraction Q31 of the total flow to pass such that QE=Q10+Q31, so long as the head loss between the upstream side and the downstream side of the screening device is less than a predetermined value, and at least one second passage (32) in the flume which is adapted to allow a fraction Q32 of the total flow to pass such that QE=Q10+Q31+Q32 when the head loss is greater than the predetermined value.