The Potomac is the longest and most diverse river system in Maryland, reaching from the cold, high plateau of the Alleghenys to the broad waters of the Chesapeake Bay and tidewater. While Great Falls is just pretty scenery for most of us, for advanced boaters, it is a runnable rapid. Great Falls is a series of falls, ranging from steep rapids to drops of over 20 feet. To navigate your route, there are observation decks on both sides of the river. Most runs are done at lower water levels found between mid-June and November. To run the falls you must register in advance with the Maryland Department of Natural Resources. You may only approach the falls from downstream, carrying your boat up over the rocks and cliffs.