The Bailey Bridge was originally designed to be capable of use as a floating bridge using Bailey components and special pontoons with attachment points on the gunwhales. I don't know if the particular 'pontoon boat' pictured is one of these or not, but the Bailey system covered the full range of bridging, from low capacity floating bridges to Triple Storey high loading bridges and Extra Wide Bailey Bridges (EWBB) and even Bailey suspension bridges.
The most common was the standard Bailey 'single single' (BSS) bridge.
The system was incredibly variable in application, all the while using standardised 'quick-clip/peg-together' components.
Mike