Rocky Gap State Park is a gorgeous mountain lake just south of River Mountain in Maryland. The park office rents canoes and kayaks for the day, based on availability. Please call the park office in advance to check on weather and rental status.
Rocky Gap State Park Office: (240) 357-4404
Rocky Gap State Park Website: https://dnr.maryland.gov/publiclands/pages/western/rockygap.aspx

Another option for kayak and canoe rentals is Shawnee State Park, just west of Bedford.
Shawnee State Park Office: (814) 733-4218
Shawnee State Park Website: https://www.dcnr.pa.gov/StateParks/FindAPark/ShawneeStatePark/Pages/default.aspx