Two kinds of water show up on this pack. Rathbun, Red Rock and Saylorville are impoundments, which means the level is something a person decides, and the shoreline you launched against in June is not always the one waiting for you in September. Spirit Lake, Clear Lake, Storm Lake and Lost Island hold a steadier edge, and what moves on them is the wind. Clear Lake covers 4,349 acres with a long fetch across it, so the ride back at four in the afternoon is a different trip from the one out at seven in the morning.
The pack carries 2,113 charted water bodies. Of those, 658 carry a name, and 87 of the named ones cover more than a square kilometer, which is about 247 acres. The largest the pack carries is Rathbun Lake, 55.8 square kilometers, or 13,788 acres. The outlines come from the National Hydrography Dataset and the depth under them is built from state elevation surveys, because there is no NOAA chart for a reservoir.
The 2,113 figure is the full set of charted water inside the box, from Rathbun down to farm ponds and oxbows off the river. Naming thins that out to 658. The number that matters most for planning is the 87 named lakes over a square kilometer, because those are the ones where getting from the ramp to where you want to be is a real question instead of a straight line you can see the end of.
Under a square kilometer, you take in the whole basin from the launch and the job is finding the deep side of it. Over that, the wind has room to work, the far bank is a decision, and the old channel starts to matter. Every one of them is charted the same way, so the small water behaves exactly like the big water once your draft is on it.
| Lake | Charted surface area |
|---|---|
| Rathbun Lake | 56 km² (13,788 acres) |
| Lake Winneshiek | 36 km² (8,920 acres) |
| Lake Red Rock | 35 km² (8,575 acres) |
| Spirit Lake | 22 km² (5,436 acres) |
| Saylorville Lake | 22 km² (5,387 acres) |
| Clear Lake | 18 km² (4,349 acres) |
| Storm Lake | 12 km² (3,089 acres) |
| Spring Lake | 12 km² (2,842 acres) |
| Albert Lea Lake | 11 km² (2,644 acres) |
| Okamanpeedan Lake | 9 km² (2,224 acres) |
| Ocheda Lake | 8 km² (1,927 acres) |
| Lake Odesa | 7 km² (1,730 acres) |
The twelve largest named lakes the Iowa pack carries, by charted surface area, measured from the chart polygon itself. The pack carries 2,113 charted water bodies in all, 658 of them named, and 87 named lakes larger than one square kilometer.
A lake is not the sea. There is no NOAA chart for Red Rock and no tide to report on it, so inland depth in Helm is built from state elevation surveys instead, and the water bodies themselves come from the National Hydrography Dataset. Those two together are the whole reason a reservoir is charted water here rather than a blue shape with a name on it. You get contours across the basin, a depth number on the water, and your own draft shading the parts the boat cannot cross.
Then there is the level. An impoundment sits at whatever the dam is holding that week, so a contour on Rathbun or Red Rock is a line drawn at a reference level and the pool is somewhere above or below it on the day you back down the ramp. Read it that way and it does a lot of work for you. With the water down, the edge sits inside the drawn shoreline, the flat at the mouth of a cove you idled over in spring is dry ground, and the old creek channel is the only way into the back of it. With the pool up, that same contour is telling you how much you have over the timber.
Every reading carries the date its survey was taken, which is the thing worth a look before you trust a thin number in an arm you have not run before.
Rathbun Lake is the largest the pack carries at 13,788 acres, better than half again the size of Lake Red Rock at 8,575. Lake Winneshiek falls between the two at 8,920. After that the list tightens up fast. Spirit Lake at 5,436 acres and Saylorville at 5,387 are within fifty acres of each other, which is the same quantity of water held two completely different ways. Clear Lake at 4,349 and Storm Lake at 3,089 come next.
Some of this water sits in more than one pack. The packs are cut to a box rather than to a state line, so Lake Winneshiek, Albert Lea Lake at 2,644 acres and Okamanpeedan Lake at 2,224 all appear here and in a neighboring pack as well. If you run border water, take whichever pack covers the ramp you launch from, and there is nothing to stop you keeping both on the phone.
Further down, the sizes start doubling up on each other. Lost Island Lake and Rice Lake measure the same to the acre off the chart polygon, 1,137 apiece. Lake Panorama is 1,161 and Trumbull Lake is 1,063, so those four are one another's twins for practical purposes. Spring Lake at 2,842 acres is more than double any of them.
The ramp on a Tuesday morning is not where you want to learn that the phone has one bar. The pack downloads at home on wifi, and once it is on the device the contours, the draft shading, the routing, the measure tool and the anchor alarm all keep working with no service at all.
The satellite chart style earns its keep the first time you launch somewhere new. On an impoundment where every wooded bank looks like the last one from the water, the picture and the contours together tell you more than either one does on its own.
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.
Real depth. Inland depth in Helm is built from state elevation surveys, so both carry contours across the basin and a depth number on the water rather than a flat outline, and each reading shows the date its survey was taken. Enter your draft once and Helm shades the water your boat cannot cross and plans a route around it.
Read them as lines at a reference level, then put the day's level against them. With the water down, the edge of the lake sits inside the drawn shoreline, the flats at the mouths of the coves come out first, and the old creek channel is the line that still has water in it. Run the measure tool down that channel and you get the shallowest point on the line instead of an average, which is the number that decides whether you go in.
The packs are cut to a box rather than to a state line, so border water like Okamanpeedan at 2,224 acres, Albert Lea Lake at 2,644 and Lake Winneshiek at 8,920 lands in more than one pack. Whichever pack covers the ramp you launch from will do the job. If you fish both ends of a border lake, keep both on the device and you have the whole thing wherever you are on it.
Helm Boating