But the rain tax will do little to affect water quality in the bay since it doesn't address what many believe is the estuary's most significant issue. The Conowingo Dam was built in 1928 as part of a hydro-electric power project and is still a working unit, now owned by Exelon. The dam is located where the Susquehanna River empties into the bay, a mere 10 miles south of the Mason-Dixon Line. Upon completion, the water behind the dam was about 120 feet deep. Nearly a century later, it is filled with sludge from the northern states in the Susquehanna Watershed, leaving only 15 to 20 feet of water on top.