A system to retrieve a buoyant leak detector (76) traveling with the fluid flowing in a pipeline (24), includes a catchment device (38) located above the bottom interior of the pipeline. Flexible, elongate manifold structures (30) are constructed with fluid outlet openings (54) extending along the manifold structures. The manifold structures are deployable to lie across the lower inside perimeter of the pipeline, upstream from the catchment device. A source of pressurized air is routed to the manifold structure, whereby air bubbles are emitted from the nozzles of the manifold structure to form a sheet or curtain of air bubbles that flow in the direction downstream of the fluid flow in the pipeline and at an angle upwardly from the location of the manifold structures to cause the leak detector to be deflected by the bubble curtain toward the catchment device.