There is a beautiful beach on the Chester River where, as kids, we learned to sail and swim. The site is called "Conquest Beach."
Williston Lake is located in Caroline County. I used to swim there as a teen. Now there are "no swimming" signs posted every where - the disadvantage of living in a litigious society.
This is the Schooner Sultana, sailing on the Chester River in Queen Anne's County and near Chestertown, Maryland.