Two kinds of water sit in this pack. The Missouri mainstem holds Lake Oahe, Lake Sharpe, Lake Francis Case and Lewis and Clark Lake, one impoundment after another, water wide enough that a crossing is a decision and the wind after noon is the thing you plan around. Oahe measures 178,731 acres off the chart polygon. Northeast of the river the lakes get smaller and sit closer together, Lake Thompson at 13,813 acres, Lake Poinsett at 9,736, Lake Kampeska at 5,041, near enough to each other that you pick one in the morning.
The pack carries 10,800 charted water bodies, which is fifth among the 48 state packs. Of those, 1,180 carry a name, and 161 of the named ones are larger than one square kilometer. The outlines come from the National Hydrography Dataset and the depth under them is built from state elevation surveys, so a lake here has contours, a depth number on the water itself, and shading read against the draft you entered.
At 10,800 charted water bodies, this pack sits fifth among the 48 state packs. Four carry more. Most of that count never sees a boat. It is what the hydrography dataset holds as water inside the box the pack is cut to, from the mainstem reservoirs down to sloughs with no road to them.
Names run differently. 1,180 of those water bodies carry one, which is 29th of the 48, and the distance between fifth and 29th is the northeast quarter of the map, where the country is full of small basins holding water that nobody ever needed to name.
The third figure is the one to plan around. 161 named lakes cross a square kilometer, 14th of the 48, and that is roughly the set you would hitch a trailer for. One thing to know about how the packs are built: they are cut to a box rather than to the state line, so water near an edge shows up in a neighboring pack as well.
| Lake | Charted surface area |
|---|---|
| Lake Oahe | 723 km² (178,731 acres) |
| Lake Francis Case | 331 km² (81,767 acres) |
| Lake Sharpe | 235 km² (58,045 acres) |
| Lewis and Clark Lake | 101 km² (24,982 acres) |
| Lake Thompson | 56 km² (13,813 acres) |
| Big Stone Lake | 48 km² (11,812 acres) |
| Lake Traverse | 43 km² (10,675 acres) |
| Lake Poinsett | 39 km² (9,736 acres) |
| Bitter Lake | 32 km² (7,809 acres) |
| Dry Lake Number Two | 26 km² (6,400 acres) |
| Belle Fourche Reservoir | 24 km² (6,054 acres) |
| Waubay Lake | 22 km² (5,535 acres) |
The twelve largest named lakes the South Dakota pack carries, by charted surface area, measured from the chart polygon itself. The pack carries 10,800 charted water bodies in all, 1,180 of them named, and 161 named lakes larger than one square kilometer.
Lake Oahe is the largest named lake the pack carries, 723.3 square kilometers, 178,731 acres, measured from the chart polygon itself. Lake Francis Case is next at 330.9 square kilometers, 81,767 acres. Then Lake Sharpe, 234.9 square kilometers and 58,045 acres, and Lewis and Clark Lake at 101.1 and 24,982 acres. Add those three together and the total is still smaller than Oahe on its own.
Water at that scale moves the work to before the launch. You are choosing which arm to run and what hour to be back at the ramp. Draw a line across a bay with the measure tool and you get distance, bearing and a depth profile along it, with the shallowest point marked rather than averaged. Enter your draft once and the water your boat cannot cross shades, which on a lake is what puts a flat on the screen while there is still room to turn.
There is no NOAA chart for a reservoir. Nautical charts are made for the water ships use, so the depth under Lake Sharpe has to come from somewhere else. Inland depth in Helm is built from state elevation surveys, laid against water body outlines from the National Hydrography Dataset. That pairing is the reason a reservoir is charted water here instead of a blue shape with a name on it, and it is what lets you plan a route across one against your own draft.
The second thing to carry in your head is that a reservoir sits at whatever level it is being held at. The basin does not move. The surface does. A contour you read in June is the same shape in October with a different amount of water standing on it, so the habit worth having is to know the pool level the day you launch and to read the contours as the shape of the bottom. Helm shows the survey date beside the reading, so you can see how old the measurement under you is.
Creek channels are where this shows up first. The old channel stays open as the water comes down and the flats on either side of it do not, and with a draft entered those flats shade on the chart before you are on top of them. A rock point that is a landmark at full pool reads the same way once the level drops.
Lake Thompson is the largest of the lakes off the mainstem at 55.9 square kilometers, 13,813 acres. Big Stone Lake and Lake Traverse come next at 11,812 and 10,675 acres, both of them close enough to a pack edge that they appear in a neighboring pack too. For scale, Lake Kampeska at 5,041 acres would fit inside Lake Oahe about thirty five times.
Below that the figures bunch up. Lake Andes and Angostura Reservoir come out identical, 19.1 square kilometers and 4,720 acres each. Lake Whitewood is 4,448 acres, Swan Lake 4,300, Columbia Road Reservoir 4,201 and Shadehill Reservoir 3,781. At that size the difference between one lake and the next is the shape of the basin rather than the size of it, which is an argument for looking at the contours before you decide where to launch. Download the pack at home and the charts, the depth shading, routing and the measure tool all keep working at a ramp with no signal.
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. Oahe is the largest named lake the South Dakota pack carries, 723.3 square kilometers and 178,731 acres measured from the chart polygon. Its depth is built from state elevation surveys rather than from a NOAA chart, so the water has contours, a depth number on it and shading against the draft you entered.
Read them as the shape of the basin, which does not change, and keep the pool level in mind as the amount of water standing on top of it. Helm shows the survey date next to the reading so you know how old the measurement is. With your draft entered, the flats on either side of an old creek channel shade while the channel stays open, and on 81,767 acres that is the part you want to see from a distance.
It carries 10,800 charted water bodies, fifth among the 48 state packs. Of those, 1,180 are named and 161 are larger than a square kilometer, which takes in Lake Thompson at 13,813 acres, Big Stone Lake at 11,812, Lake Traverse at 10,675, Lake Poinsett at 9,736, Waubay Lake at 5,535 and Lake Kampeska at 5,041.
Helm Boating