Most days on this water start at a ramp on a reservoir. Carlyle Lake is the largest the pack carries, 22,684 acres, and Lake Shelbyville at 10,181 acres would fit inside it twice over with room to spare. Upper Peoria Lake measures 15,370 acres and Crab Orchard Lake 7,265. Below that tier the names on the chart get less famous and a good deal more interesting, because they run to sloughs, backwaters, ponds and a cooling pond at a power plant, and most of them have a ramp on them somewhere.
The pack carries 5,368 charted water bodies. Of those, 1,543 are named, and 118 of the named ones are larger than a square kilometer, which is about 247 acres. Set against the other 47 state lake packs, that is sixteenth by water bodies, eighteenth by named water and nineteenth by lakes over a square kilometer, so all three land in the upper half. The outlines come from the National Hydrography Dataset and the depth under them is built from state elevation surveys, which is the reason a reservoir here is charted water instead of a blue shape with a name printed on it.
Helm splits inland lake coverage into 48 state packs. This one is sixteenth by charted water bodies, eighteenth by named water and nineteenth by named lakes over a square kilometer. Three ranks sitting inside four places of each other says something about the shape of the water here. There is no single enormous lake dragging a count upward. There is a lot of water, spread out, most of it modest in size.
Of the 5,368 water bodies in the pack, 3,825 carry no name on the chart. They still have an outline, and an outline is the thing a depth surface gets draped over. An unnamed oxbow off a river bend is charted water the same way Carlyle is.
Of the 1,543 named waters, only 118 clear a square kilometer. The other 1,425 come in under 247 acres, which is the size of water a lot of people fish on a weeknight.
| Lake | Charted surface area |
|---|---|
| Carlyle Lake | 92 km² (22,684 acres) |
| Mine Number 21 Reservoir | 69 km² (16,976 acres) |
| Upper Peoria Lake | 62 km² (15,370 acres) |
| Lake Shelbyville | 41 km² (10,181 acres) |
| Crab Orchard Lake | 29 km² (7,265 acres) |
| Senachwine Lake | 22 km² (5,412 acres) |
| Lake Geneva | 22 km² (5,387 acres) |
| Lake Clinton | 18 km² (4,571 acres) |
| Lake Springfield | 16 km² (3,880 acres) |
| Horseshoe Lake | 13 km² (3,188 acres) |
| Spring Lake | 12 km² (3,089 acres) |
| Broad Pond | 12 km² (2,916 acres) |
The twelve largest named lakes the Illinois pack carries, by charted surface area, measured from the chart polygon itself. The pack carries 5,368 charted water bodies in all, 1,543 of them named, and 118 named lakes larger than one square kilometer.
There is no NOAA chart for a reservoir. NOAA charts the coast, the intracoastal and navigable rivers, and an impoundment well inland is outside all of it. Inland depth in Helm comes from state elevation surveys instead, and the water bodies come from the National Hydrography Dataset. The survey describes the shape of the ground. The hydrography describes where the water sits on it. That pairing is the whole reason a lake in this pack is water you can plan a route across against your draft.
A reservoir also sits at whatever level it is being held at. Summer pool, a winter drawdown, a week of rain upstream and a gate opened somewhere below: the level moves, and every contour on the lake moves with it. A contour that read four feet at summer pool has less than four feet over it once the lake is pulled down, and the cove you idled through in June is a place to trim up and crawl in October.
So read a contour on a reservoir against the pool the lake is being held at today, and treat it as the shape of the bottom rather than a promise about the surface. The bottom is the part that does not move. How the shading works, how your draft becomes part of the chart and how a route gets planned around water you cannot cross are covered on the depth and routes pages. None of that changes inland. What changes is where the number underneath it came from.
Carlyle Lake is the largest named water the pack carries, 91.8 square kilometers, or 22,684 acres. Mine Number 21 Reservoir is next at 16,976 acres, and Upper Peoria Lake after that at 15,370. Lake Shelbyville, which nobody would call small, comes in at 10,181.
Below the top four the drop is steep. Crab Orchard Lake is 7,265 acres. Senachwine Lake is 5,412 and Lake Geneva 5,387, which puts 25 acres between them. Then Lake Clinton at 4,571, Lake Springfield at 3,880, Horseshoe Lake at 3,188 and Spring Lake at 3,089. Lake Decatur is 2,891 and Kinkaid Lake 2,323, and Kinkaid at that size is about a tenth of Carlyle. All of these figures are measured off the chart polygon itself, so they are the surface the chart actually draws rather than a number from a brochure.
Names near a state line turn up in more than one pack. The packs are cut to a box rather than to the state line, so water over toward the Wisconsin, Iowa, Missouri or Kentucky side can sit in two packs at once. Lake Geneva is one of those. If the water you run is near a border, the pack next door carries it as well, and the coverage overlaps instead of stopping at the line.
Some of the larger named water in this pack is not what most people picture when they hear the word lake. Broad Pond is 2,916 acres. Cross Slough is 2,768. Quiver Lake and the Braidwood Power Plant Cooling Pond are both 2,520 acres to the acre, which is a coincidence and nothing more, and is still the sort of thing you notice reading down a chart list. Here is that whole band, the named water in the pack between roughly 2,400 and 3,000 acres:
Water like that is charted the same way the big reservoirs are. It has an outline from the hydrography dataset and a depth surface from the state elevation survey, so shallow water in it shades as shallow water. Nine of the twenty largest named waters in this pack are under 3,000 acres, which is a size you can cross in a few minutes and still run aground 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.
It has contours. Carlyle is the largest named water the pack carries, 91.8 square kilometers, or 22,684 acres, and inland depth comes from state elevation surveys rather than from a NOAA chart, so there are contours and a depth number on the water itself, read against the draft you entered.
Because the lake is held at a level and that level moves. Shelbyville covers 10,181 acres at the chart polygon, and the contours under it come from a state elevation survey of the lake bed, which does not change when the pool is drawn down. The bottom stays where it is. The water over it does not. Read the contour against the pool the lake is sitting at that week and give yourself the difference.
Both can. The packs are cut to a box rather than to a state line, so water near a border appears in more than one of them. Lake Geneva is in this pack at 21.8 square kilometers, or 5,387 acres, within 25 acres of Senachwine Lake in the same list. If the water you run is near the line, download the neighboring pack as well and the two overlap.
Helm Boating