The dam is named for the town of Conowingo, Maryland. The original location of Conowingo is now under the waters of the reservoir created by the dam. The town was relocated during construction of the dam to its present location about 1 mile northeast of the dam's eastern end. The area, as per the 1612 John Smith map, was originally known as Smyth's Falls.
Conowingo Dam also serves as a bridge for U.S. Route 1 across the Susquehanna River. The original Route 1 crossing, Conowingo Bridge, would have been submerged after the completion of the dam, so it was demolished in 1928. The Conowingo Reservoir, and the nearby Susquehanna State Park, provide many recreational opportunities.
Eleven turbine sites were constructed but only seven turbines were initially installed, driving generators each rated for 36 megawatts. A turbine house, on the southwestern end of the dam, encloses these seven units. One additional "house" unit provides 25 Hz power for the dam's electric railroad system (identical to that used by the Pennsylvania Railroad, who had an electrified line [now under Norfolk Southern ownership] running on the eastern shore). In 1978, four higher capacity turbines were added. Each drives a 65 megawatt generator, increasing the dam's electrical output capacity from 252 to 548 megawatts. The four newer turbines are in the open air section at the northeast end of the power house. The generators produce power at 13,800 volts. This is stepped up to 220,000 volts for transmission, primarily to the Philadelphia area. The dam currently contributes an average of 1.6 billion kilowatt hours annually to the electric grid.
In 1936, all the flood gates were opened. During Hurricane Agnes, in 1972, all 53 flood gates were opened, for only the second time, and explosives planted to blow a section of the weir, as the waters rose during the early morning hours of June 24 within five feet of topping the dam (a record crest of 111.5 ft or 33.98 m., three feet above normal level for the entire 14 mile long Conowingo Reservoir.) Paul English, dam superintendent, released a bulletin at 10:30 p.m. on June 23 saying that the water levels were reaching a point at which the stability of the dam "cannot be controlled. When it reaches 111 feet...it will be in the hazy area...It is not known...whether a structure of the dam may give and...people downstream should be advised. At this time, the flow sensor in the dam recorded its record discharge of 1,130,000 ft3/s (32,000 m3/s), and the flood gauge at the dam registered a record . On January 20, 1996, the gauge recorded its second-highest recorded crest of . A severe ice jam also developed behind the dam on this date. The record minimum recorded discharge was on March 2, 1969, when the flow sensor registered 144 ft3/s (4.07 m3/s).
The Conowingo Dam, and to a lesser extent the Holtwood and Safe Harbor Dams further upstream, severely impacted the migratory fish species, especially American shad, that would swim up the Susquehanna River to spawn. In 1984 a fish capture feature was added at Conowingo and the Shad were trucked upstream above all three dams and released. This program ended in 1999. A fish lift was installed in 1991. All three dams completed installation of fish lifts in time for the 2000 season. During the 2000 migration season, 153,000 American shad passed through the Conowingo fish lift. "However, passage rates of shad from Conowingo to Holtwood have been only 30 to 50 percent, suggesting that fish are having difficulty moving upstream in the waters of the Conowingo pool.
The three dams are also involved with another ecological concern. Normally the reservoirs above each dam trap sediment and nutrients that run off from the watershed and prevent some of that from reaching the Chesapeake Bay. A recent USGS study suggests that there may be as little as 20 years left before they reach capacity and no longer function to reduce the nutrient and sediment load hitting the bay. However the scouring of major floods, and other factors, affect this.