Maryland’s Lakes and Reservoirs: FAQ

Q1: Is it true that Maryland does not have any natural lakes?
A1: Yes, there are no natural lakes in Maryland. All of Maryland’s lakes are manmade by damming rivers. Some have been named lakes (e.g., Lake Habeeb in Allegany County and Deep Creek Lake in Garrett County), but most have been named reservoirs (e.g., Loch Raven Reservoir in Baltimore County).

Q2: Did Maryland ever have any natural lakes in the past?
A2: Yes. We know of at least one, and there could be more. The one clearly documented case is Buckel’s Bog, which was a 160-acre, shallow periglacial lake (actually a glade) that occupied the headwater region of the North Branch of the Casselman River in Garrett County during the late Pleistocene (19,000-14,000 years ago). [Reference: Maxwell, J.A. and Davis, M. B., 1972, Pollen evidence of Pleistocene and Holocene vegetation of the Allegheny Plateau, Maryland: Quaternary Research, 2(4): 506-530.]

Q3: Why are there no natural lakes in Maryland?
A3: There are about a dozen major types of lakes, meaning there are about a dozen ways lakes form. None of those is found in Maryland. Some 74% of all lakes are glacial in origin, but glaciers never entered Maryland during the last Great Ice Age. Glacial lakes may form in bedrock depressions gouged out by glaciers or in areas where detached blocks of stagnant or retreating ice sheets are surrounded by other glacial deposits, such as sand and gravel outwash. When the blocks of ice melt away, the remaining depression, known as a kettle, may fill with water to form a “kettle lake.” Other major types of natural lakes include those that result from faulting, volcanic activity, and landslides blocking a river.

Q4: Why are some manmade lakes called lakes while others are called reservoirs?
A4: There are no hard and fast rules about naming. However, in general, the primary use of the manmade lake/reservoir determines what the body of water is called. If the primary use is recreation, the body is often called a lake (e.g., Deep Creek Lake, Greenbrier Lake, and Lake Linganore). If the primary use is water supply, hydroelectric power, and/or flood control, the body is more likely called a reservoir (e.g., Prettyboy Reservoir, Loch Raven Reservoir, and Triadelphia Reservoir).

Q5: What are some characteristics of the larger reservoirs or lakes in Maryland?
A5: The following table summarizes some of the main characteristics of those reservoirs in Maryland that have a surface area greater than one square mile. They are listed in the order of decreasing surface area.

Name	County	River affected	Primary Purpose	Surface Area (acres) ¹	Max. Capacity (acre ft.) ²
Conowingo Reservoir	Harford & Cecil Counties + Pa.	Susquehanna River	Hydroelectric	8,563	310,000
Deep Creek Lake	Garrett County	Deep Creek (a tributary of the Youghiogheny River)	Hydroelectric & recreational	3,900	103,350
Liberty Reservoir	Baltimore & Carroll Counties	North Branch Patapsco River	Baltimore City water supply	3,106	177,000
Youghiogheny River Reservoir	Garrett County + Pa. (mostly in Pa.)	Youghiogheny River	Flood control & hydroelectric	2,800	151,200
Loch Raven Reservoir	Baltimore County	Gunpowder River	Baltimore City water supply	2,400	91,900
Prettyboy Reservoir	Baltimore County	Gunpowder Falls	Baltimore City water supply	1,500	90,100
Jennings Randolph Lake	Garrett County	North Branch Potomac River	Potomac River Flood control	952-965	130,900
Triadelphia Reservoir (Brighton Dam)	Montgomery County	Patuxent River	Hydroelectric	800	32,300
Rocky Gorge	Montgomery County	Patuxent River	Washington area water supply	773	22,000
Notes There are 640 acres in 1 square mile. To find the surface area in square miles, divide the number of acres by 640. There are 43,560 square feet in 1 acre. To convert acre-feet to cubic feet, multiply the number of acre-feet by 43,560.

Downloads and Links

FactSheet 15: Maryland’s Lakes and Reservoirs: FAQ (pdf, 14 kb).

Other information on Maryland lakes: Bathymetric maps of Maryland reservoirs

Prepared by Jim Reger
Compiled by the Maryland Geological Survey, 2300 St. Paul Street, Baltimore, MD 21218
This electronic version of "Fact Sheet No.15" was prepared by R.D. Conkwright, Division of Coastal and Estuarine Geology, Maryland Geological Survey. Please send comments on this page to Dale Shelton (dshelton@dnr.state.md.us)