There are several waste weirs on the Chesapeake and Ohio Canal, and they are marked by small concrete bridges that cross channels exiting the canal. However, in the case of this pumping station, the little bridge is crossing a flume–of sorts–entering the canal. There is an interesting story regarding this pumping station, and I will paraphrase from the Mason-Dixon Council Boy Scouts of America’s 184 Miles of Adventure–a great little book available at the C&O’s visitor centers.
Originally, there was a steam pump (built in 1856) located near lock 68 (close to the confluence of the North and South Branches of the Potomac) that substituted for the proposed Feeder Dam #7, which was never built. The reason for the pump was to supply water to the canal during periods of drought. Sometime later (around 1875), the pump site was switched to this location (174.18). Most canal structure types are represented by many duplicates (locks, guard locks, weirs, culverts, aqueducts, etc.), but pumping stations are few and far between.
In his Towpath Guide to the C&O Canal, Thomas Hahn describes some of the particulars regarding the station. What you see today is very little of the erstwhile structure. The engine house was originally covered by a 23′ x 23′ wooden building, and there was an additional 18.5′ x 32′ brick boiler room. The pump was capable of raising water 25′ from the river at the rate of 24 cubic feet per-second. Today, some of the bricks can still be seen on site.