Most of the big water in this pack was a valley first. Pymatuning Reservoir, Allegheny Reservoir, Raystown Lake and Lake Wallenpaupack all sit behind dams, and the shape under the boat is still the shape of the ground that was flooded. There is an old creek bed running down the middle of it, benches along the sides where the ground leveled off, and a shoreline that is only where the water happens to stop this month. That last part is what catches people out. A cove you idled through in June can be a flat you are backing off of in October, and the track you saved in the spring does not know the difference.
The Pennsylvania pack carries 3,353 charted water bodies. Of those, 1,580 carry a name, which puts the pack seventeenth of the forty-eight state lake packs for named water, and 100 of the named lakes are larger than a square kilometer. The water bodies themselves come from the National Hydrography Dataset. The depth under them is built from state elevation surveys. That combination is the reason a reservoir shows up as water you can plan a route across against your draft instead of a blue shape with a name printed over it.
The packs are cut to a box rather than to a state line, so water near a border is carried in more than one of them. Chautauqua Lake, Deep Creek Lake, Lake Hopatcong and Cheat Lake all sit in this pack and in a neighboring pack as well. None of that changes what is on your screen at the ramp. It only means the box reaches past the line on a map.
Pymatuning Reservoir is the largest water the pack carries, at 56.0 square kilometers or 13,838 acres. Chautauqua Lake is right behind it at 53.5 square kilometers and 13,220 acres, close enough that the two of them are within about six hundred acres of each other. After Allegheny Reservoir at 12,133 acres the drop is steep. Raystown Lake, fourth on the list at 8,080 acres, is a little under three fifths the size of Pymatuning, and Lake Wallenpaupack at 5,436 acres is not much more than a third of it. By the time you reach Lake Arthur at 3,064 acres you are on water you can cross in a few minutes.
These figures are measured off the chart polygon itself, which is the same outline the app draws.
| Lake | Charted surface area |
|---|---|
| Pymatuning Reservoir | 56 km² (13,838 acres) |
| Chautauqua Lake | 54 km² (13,220 acres) |
| Allegheny Reservoir | 49 km² (12,133 acres) |
| Raystown Lake | 33 km² (8,080 acres) |
| Lake Wallenpaupack | 22 km² (5,436 acres) |
| Cannonsville Reservoir | 19 km² (4,695 acres) |
| Deep Creek Lake | 15 km² (3,657 acres) |
| Shenango River Lake | 14 km² (3,459 acres) |
| Lake Arthur | 12 km² (3,064 acres) |
| Youghiogheny River Lake | 12 km² (2,891 acres) |
| Lake Hopatcong | 10 km² (2,471 acres) |
| Foster Joseph Sayers Lake | 7 km² (1,656 acres) |
The twelve largest named lakes the Pennsylvania pack carries, by charted surface area, measured from the chart polygon itself. The pack carries 3,353 charted water bodies in all, 1,580 of them named, and 100 named lakes larger than one square kilometer.
Counting named water, this pack sits seventeenth of the forty-eight state lake packs. Most of what makes up that count is small. Of the 1,580 named water bodies, 100 clear a square kilometer. The other 1,480 named ones sit below that size, and a further 1,773 water bodies are carried with no name on them at all.
That is the part worth knowing if you fish small water. A township pond behind a gas station, or a dam on a feeder creek nobody outside the township has heard of, is never going to turn up on a marine chart. Both are in this pack with an outline and a position on them.
It all comes down as one pack. Once it is on the phone, the chart, the depth shading and the routing keep working at a ramp with no bars, which describes a good many of the better ramps.
There is no NOAA chart for a reservoir. NOAA surveys the coast, the intracoastal and the navigable rivers, and a lake held behind a dam up in the ridges was never part of that work. So inland depth in Helm is built from a different source. State agencies survey their own water, and that elevation work is what puts contours and a depth number on a lake, matched to the water body outlines from the National Hydrography Dataset.
The two pieces do different jobs. The hydrography tells the app where the water is, down to the pond at the end of a farm lane. The elevation survey tells it what is underneath. Put those together and enter your draft and the lake stops being a picture. It becomes water with a passable side and an impassable side, which is what routing and depth shading need in order to mean anything away from the coast.
Each reading carries the date its survey was taken, so you can see how old the measurement under you is before you lean on it.
A contour on a reservoir is a measurement of the lake bed, referenced to the level the water stood at when the survey was made. The water is under no obligation to stay there. A lake that runs a generator, or one drawn down for winter storage and refilled through the spring, works through a range of levels every year, and the surface you launch onto in April is not the surface you launch onto in October.
What holds still is the bed. The old creek channel runs where it always ran, and the flat at the back of an arm is still a flat whether there is eight feet of water over it or two. Reading one of these lakes well comes down to reading that shape and then carrying a single offset in your head for whatever the pool is doing that week. The survey date next to the reading is what lets you work the offset out once and apply it everywhere instead of guessing at each spot.
With a draft entered, the shoulders on either side of the channel shade and the channel stays open. On something like Raystown Lake, where 8,080 acres of water fills a long narrow valley, that picture on the screen is the difference between running up an arm you have never been up and turning around halfway on a hunch.
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.
The pack carries 3,353 water bodies and 1,580 of them are named, so the list runs long. Among the largest are Pymatuning Reservoir at 13,838 acres, Allegheny Reservoir at 12,133 acres, Raystown Lake at 8,080 acres, Lake Wallenpaupack at 5,436 acres and Lake Arthur at 3,064 acres. Inland depth comes from state elevation surveys, so the water carries contours and a depth reading on it rather than just an outline.
The packs are cut to a box rather than to a state line, so water near a border is carried by more than one of them. Chautauqua Lake at 13,220 acres, Deep Creek Lake at 3,657 acres, Lake Hopatcong at 2,471 acres and Cheat Lake at 1,359 acres all fall inside this box and inside a neighboring state pack as well. Take whichever pack covers the ramp you launch from and that water will be on the chart.
They describe the lake bed, referenced to the level the water stood at when the survey was made. The bed does not move when the pool does, so the old channel and the benches along it stay exactly where they are, and a pool held below the survey level means you take the same difference off everywhere on the lake. Helm shows the survey date beside the reading, so that difference is one figure you work out once rather than a fresh guess in every cove.
Helm Boating