Most of the water in this pack was put there on purpose. A dam went across a creek, the valley behind it filled, and the fence lines and the stream channel went under together. That is what is under the boat on Pymatuning Reservoir, on Mosquito Creek Lake, on Berlin Lake, on Salt Fork Lake and on a few hundred smaller ones nobody outside the county talks about. The old channel is still the deep part of the lake. The flats on either side of it were ground before they were water, and they shelve at the same gentle rate they always did. People who grew up running one of these lakes take the same lines every season for a reason.
The pack carries 2,196 charted water bodies. Of those, 718 are named, and 78 of the named lakes measure more than a square kilometer, which is about 247 acres. The largest lake the pack carries is Pymatuning Reservoir at 56.0 square kilometers, or 13,838 acres. Depth on all of it is built from state elevation surveys rather than from a nautical chart, because no nautical chart is made for a reservoir, and the water body outlines come from the National Hydrography Dataset. That combination is the difference between water you can plan a route across against your draft and a blue shape with a name printed on it.
The count is 2,196, and only 718 of those carry a name. The gap is the interesting part. Most inland water is small, and most small water has never had a name on any map: the pond behind the township garage, the backwater off a river bend, the pit that filled in and stayed. It is charted anyway. The outlines come from the National Hydrography Dataset, which does not care whether a piece of water is famous.
Of the named lakes, 78 measure over a square kilometer. That is roughly one named lake in nine. A square kilometer is also about where a lake stops being a place you idle around in an afternoon and starts being a place where the wind picks up a fetch across it and a crossing is something you think about before you make it. The rest of the named water is jon boat and trolling motor country, and it is on the chart with contours the same as the big ones.
The point of the raw count is planning at the kitchen table. If the lake you are hauling to on Saturday is one of the small unnamed ones, it still has a shape and a depth on it before you ever back down the ramp.
| Lake | Charted surface area |
|---|---|
| Pymatuning Reservoir | 56 km² (13,838 acres) |
| Grand Lake | 51 km² (12,578 acres) |
| Mosquito Creek Lake | 28 km² (6,968 acres) |
| Dunns Pond | 20 km² (5,041 acres) |
| Brookville Lake | 18 km² (4,349 acres) |
| Berlin Lake | 14 km² (3,558 acres) |
| Shenango River Lake | 14 km² (3,459 acres) |
| Senecaville Lake | 14 km² (3,459 acres) |
| Williams Lake | 13 km² (3,188 acres) |
| Salt Fork Lake | 11 km² (2,768 acres) |
| Crane Lake | 11 km² (2,743 acres) |
| Hoover Reservoir | 11 km² (2,693 acres) |
The twelve largest named lakes the Ohio pack carries, by charted surface area, measured from the chart polygon itself. The pack carries 2,196 charted water bodies in all, 718 of them named, and 78 named lakes larger than one square kilometer.
There is no NOAA chart for a lake behind a dam. The federal chart program covers the coast, the intracoastal and navigable rivers, so an impoundment out in farm country was never going to be on one. What does exist is state elevation survey work over the ground the lake sits on, and that is what Helm builds inland depth from. Pair it with the water body outlines and a reservoir becomes charted water: contours, shading, and a depth number you can read off the screen and draw a line across.
The thing worth holding in your head is what was actually measured. The survey measured the bed. The bed is the part that stays where it is. What moves is the level the lake is being held at, and a reservoir is always being held at something, whether that is a summer pool, a fall drawdown, or whatever the dam is passing after a wet week. So the old creek channel runs the same line in June and in November. The amount of water standing over the shoulders on either side of it does not.
That is the habit a reservoir asks of you, and it is why the shoulders matter more than the middle. Enter your draft once and the water your boat cannot cross shades on the chart, which on a lake that has been pulled down is exactly where you want to be looking while you still have room to turn.
Pymatuning Reservoir is the largest at 56.0 square kilometers, 13,838 acres, measured off the chart polygon itself rather than quoted from a sign at the ramp. Grand Lake is close behind at 50.9 square kilometers, 12,578 acres. Those two sit in a class of their own here. The next one down, Mosquito Creek Lake, is 28.2 square kilometers, a little over half of Pymatuning, and after that comes Dunns Pond at 20.4 square kilometers. Dunns Pond is the fourth largest piece of water in the pack at 5,041 acres and is still called a pond.
Here is the top of the list, in square kilometers as the chart polygon measures them:
Below the top ten the pack thins out gradually instead of falling off a cliff. Crane Lake is 11.1 square kilometers and Hoover Reservoir is 10.9, with Michael J Kirwan Reservoir at 10.5 right behind them, close enough together that the difference between any two of them is a couple of coves. Piedmont Lake measures 9.2 square kilometers, 2,273 acres. Tappan Lake is 8.6, and Clarence J Brown Reservoir is 8.1.
There are two exact ties in the top twenty, which is the kind of thing you only notice when the acreage is measured the same way for every lake instead of copied from whoever published it first. Shenango River Lake and Senecaville Lake both come out at 14.0 square kilometers, 3,459 acres each. Rocky Fork Lake and William H Harsha Lake both come out at 8.0 square kilometers, 1,977 acres each. Meander Creek Reservoir is 7.6, and Lake Milton closes the twenty at 6.7 square kilometers, 1,656 acres. Sixteen hundred acres is more water than most people cover in a day of fishing.
The packs are cut to a box rather than to the state line, so a lake near the edge of that box sits in this pack and in a neighboring one as well. The Michigan, Pennsylvania, West Virginia and Kentucky packs all share an edge with this one. Whichever of them is on your phone, the water near that edge is charted in it. The pack is one of 161 in Helm, and once it is downloaded the charts, the depth shading, routing and the anchor alarm keep working at a ramp where the signal quit a mile back up the gravel.
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.
Pymatuning Reservoir, at 56.0 square kilometers or 13,838 acres measured from the chart polygon. Grand Lake is second at 50.9 square kilometers, 12,578 acres, and Mosquito Creek Lake is third at 28.2 square kilometers, 6,968 acres. Because the packs are cut to a box rather than to the state line, a lake sitting near the edge appears in this pack and in the neighboring one too.
Real depth. Inland lake depth is built from state elevation surveys and the water body outlines come from the National Hydrography Dataset, so Salt Fork Lake at 2,768 acres and Hoover Reservoir at 2,693 acres carry contours and a depth number on the water, shaded against the draft you enter for your own boat. The pack does this for all 2,196 water bodies it carries, not only the named ones.
Because the survey behind it measured the lake bed, and the bed is not the thing that changes. A reservoir sits at whatever level it is being held at, so when the pool is down in the fall there is less water standing over the shoulders of the old creek channel than there was at summer pool. The channel itself runs the same line all year. With your draft entered, the shading is what shows you where those shoulders come up.
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