Looks like the reservoir may be open later than through the end of the 2016 season as originally stated. Info from NOVA Parks:
Beaverdam Reservoir, owned by Loudoun Water, is first and foremost a source of public drinking water. Loudoun Water has partnered with the Northern Virginia Regional Park Authority (NOVA Parks) to manage recreational activities and public access until the spring/summer of 2017. At that time it will close to complete needed repairs to the infrastructure. After repairs are complete, expected to take approximately 1.5 to 2 years, the property will reopen for public access under the management responsibilities of NOVA Parks.