Most of the water worth putting a boat on around here was a river valley before somebody built a dam at the bottom of it. Liberty Lake and Loch Raven Reservoir both have that shape, and so does Prettyboy Reservoir. A drowned creek bed runs down the middle, arms reach up every side draw, and the old banks of that creek stand off the bottom as edges worth fishing. Deep Creek Lake is the largest named lake the pack carries, at 3,657 acres. Running any of them is a different problem from running the bay. The deep line is wherever the stream used to be, and the shallow is a hillside somebody used to walk on.
The pack holds 878 charted water bodies. Of those, 359 carry a name, and 25 of the named lakes are larger than a square kilometer. The outlines come from the National Hydrography Dataset, and the depth beneath them is built from state elevation surveys. That is what makes a reservoir open as charted water with contours on it, instead of a blue shape with nothing inside.
The count is 878 charted water bodies, and 359 of them carry a name. The other 519 arrive with no name in the source data, which is not the same as arriving with nothing on them. A pond with no label still has an outline you can measure across and depth shading that answers to the draft you entered.
A square kilometer is about 247 acres. The 25 named lakes above that line are the ones with enough open water that the tow is worth doing, and they are the lakes most people mean when they talk about boating on this water. Everything under it is the water you already know, the small impoundment twenty minutes from the house that nobody ever surveyed for you.
Small water is where having a chart at all changes the day. Draw a line from the ramp to the far bank and you get distance, bearing and a depth profile along it, with the shallowest point marked rather than averaged into the rest.
| Lake | Charted surface area |
|---|---|
| Deep Creek Lake | 15 km² (3,657 acres) |
| Liberty Lake | 12 km² (2,916 acres) |
| Youghiogheny River Lake | 12 km² (2,891 acres) |
| Loch Raven Reservoir | 9 km² (2,199 acres) |
| Prettyboy Reservoir | 6 km² (1,507 acres) |
| Occoquan Reservoir | 5 km² (1,285 acres) |
| Lake Marburg | 5 km² (1,161 acres) |
| Mount Storm Lake | 4 km² (1,112 acres) |
| Jennings Randolph Lake | 3 km² (815 acres) |
| Triadelphia Reservoir | 3 km² (791 acres) |
| Lake Manassas | 3 km² (692 acres) |
| Rocky Gorge Reservoir | 3 km² (642 acres) |
The twelve largest named lakes the Maryland pack carries, by charted surface area, measured from the chart polygon itself. The pack carries 878 charted water bodies in all, 359 of them named, and 25 named lakes larger than one square kilometer.
NOAA surveys the coast. It does not survey Prettyboy Reservoir, and there is no nautical chart for an impoundment, so inland depth in Helm is built from state elevation surveys instead. The water bodies come from the National Hydrography Dataset. Those two sources together are the reason Liberty Lake opens with contours on it and a depth number you can hold your draft against, rather than as an outline.
A reservoir also sits at whatever level it is being held at that week. The contours describe the shape of the basin, and the basin does not move. The water on top of it does. When the pool is drawn down, every contour sits nearer the surface than the chart's own reference, and the shoreline stands inside the line the chart draws. The habit worth keeping is to check what the lake is being held at before you leave the house, then carry that offset in your head all day and read every number on the screen against it.
Drawdown is also why the shoulder of a creek channel is the thing to watch on a reservoir rather than the middle. With a draft entered, the channel stays open on the screen and the shoulders on either side shade, which is where a low pool puts stumps and old fence lines within reach of a lower unit. Each depth reading carries the date of the survey it came from, so you can see how old the measurement under you is.
Deep Creek Lake is the largest named lake the pack carries, at 14.8 square kilometers, or 3,657 acres. Below it the sizes bunch up quickly.
Liberty Lake and Youghiogheny River Lake are 25 acres apart, which on the water is no difference at all. Loch Raven Reservoir, at 2,199 acres, is about three fifths of Deep Creek. Triadelphia Reservoir and Rocky Gorge Reservoir together come to 1,433 acres, still short of Prettyboy Reservoir on its own at 1,507. Farther down the list, Little Seneca Lake and Lunga Reservoir come out identical at 469 acres each, and Goose Pond and Beaverdam Reservoir both measure 297. The twenty largest named lakes the pack carries end at Piney Run Lake, 272 acres.
What that bunching means in practice is that the choice between the second and third largest water here is a question of which ramp is closer, not which lake is bigger.
Chart packs are cut to a rectangle, so a lake near a border belongs to more than one of them. That is why Occoquan Reservoir at 1,285 acres, Lake Manassas at 692 and Lunga Reservoir at 469 are all carried here and also appear in the Virginia pack. Mount Storm Lake at 1,112 acres and Jennings Randolph Lake at 815 are shared with West Virginia. Lake Marburg at 1,161 acres, Youghiogheny River Lake at 2,891 and Octoraro Lake at 618 are shared with Pennsylvania. Delaware is the fourth neighbor whose box overlaps this one.
The useful part of that arrangement is what happens on a border lake. Whichever of the two packs you downloaded, the whole lake comes with it, both shorelines and the water in between, so a route that crosses the line does not run off the edge of your chart halfway across.
It also means the lake list above is a list of what this pack carries and nothing more. A lake being in it says where the box falls, not who the water belongs to, and the people who launch on Octoraro every weekend already know which side of it they park on.
Inland lake depth comes from state elevation surveys rather than from nautical charts, and a reservoir sits at whatever level it is being held at that week. Treat the shape and the depth as a guide, keep a lookout, and verify locally.
Yes. Deep Creek Lake is the largest named lake the pack carries, 14.8 square kilometers or 3,657 acres, and it opens with depth contours built from state elevation surveys rather than as a plain outline. Enter your draft and the water your boat cannot cross shades, so the flats at the back of the coves read differently from the old channel.
878 charted water bodies. 359 of them carry a name, and 25 of those named lakes are larger than a square kilometer, which is about 247 acres. The rest are the small impoundments and ponds, and they are charted too, with an outline you can measure across and depth shading on the water.
Because the packs are cut to a rectangle rather than to a state line, so a lake near a border sits in two of them. Occoquan Reservoir at 1,285 acres and Lunga Reservoir at 469 are shared with the Virginia pack, Mount Storm Lake at 1,112 acres and Jennings Randolph Lake at 815 with West Virginia. Either pack gives you the whole lake, not the half on one side of the line.
Helm Boating