Lake Winnebago covers 131,213 acres. That is enough water for the wind to have room to work before it reaches you, and a Saturday out there is not the same job as a Saturday on Green Lake at 9,341 acres or up on the Turtle-Flambeau Flowage. Then there is the river water. Lake Pepin is a widening of the Mississippi and Lake Onalaska is a pool above a lock, and both of them behave like the river they belong to more than like a lake. The water in this pack does a lot of different jobs, and the pack has to carry all of them.
It carries 8,757 charted water bodies. 5,612 of those have a name, which puts it third among the 48 state lake packs, and 478 of them are named lakes larger than a square kilometer, which is fourth. The depth under all of it is built from state elevation surveys, and the water bodies themselves come from the National Hydrography Dataset. That is the reason a flowage in the middle of the state is charted water in Helm rather than a blue shape with a label on it.
By raw count the pack ranks ninth of the 48 state lake packs, and that is the least interesting of its three numbers. Named water is where it sits near the top. 5,612 of the 8,757 carry a name, third of 48, and 478 of them are named lakes over a square kilometer, fourth of 48. A count on its own can be padded out with unnamed farm ponds and backwater sloughs. This one is not padded, which matters the moment you go looking for the lake somebody named for you at the bait shop and expect the app to know the same name.
The 478 figure is the one to hold onto if you are the sort who runs somewhere new every few weekends. That is 478 lakes big enough that you would think about wind before launching, all in a single download, and they are not clustered in one corner of the box.
| Lake | Charted surface area |
|---|---|
| Lake Winnebago | 531 km² (131,213 acres) |
| Lake Pepin | 102 km² (25,304 acres) |
| Petenwell Lake | 92 km² (22,857 acres) |
| Lake Chippewa | 60 km² (14,777 acres) |
| Lake Poygan | 57 km² (14,159 acres) |
| Lake Gogebic | 52 km² (12,973 acres) |
| Castle Rock Lake | 52 km² (12,899 acres) |
| Turtle-Flambeau Flowage | 52 km² (12,874 acres) |
| Lake Koshkonong | 43 km² (10,527 acres) |
| Lake Onalaska | 42 km² (10,453 acres) |
| Lake Mendota | 39 km² (9,736 acres) |
| Green Lake | 38 km² (9,341 acres) |
The twelve largest named lakes the Wisconsin pack carries, by charted surface area, measured from the chart polygon itself. The pack carries 8,757 charted water bodies in all, 5,612 of them named, and 478 named lakes larger than one square kilometer.
NOAA charts the coast, the intracoastal and the navigable rivers. A reservoir held behind a dam on the Wisconsin River is not on that list and never was, which is why so many apps put a lake on the screen as an outline with nothing inside it. Helm builds inland depth from state elevation surveys instead. The water body outlines come from the National Hydrography Dataset, so the shape is right, and the elevation survey is what fills it in. The outline tells you where the water ends. The survey is what your draft gets read against, and that is the difference between a blue shape and water you can plan a line across.
A flowage also sits at whatever level it is being held at that week, which is a real thing to know before you trust a contour on one. The contour is a fixed line drawn from a survey. The surface over it moves. Read the two together: the contour on the screen, and whatever the pool is being held at the day you launch, which whoever runs the dam publishes. In spring the shoulders of an old creek channel are well under you. Later in the season those same shoulders are the reason somebody is walking a boat back toward the ramp.
Lake Winnebago is the largest named lake the pack carries, at 531.0 square kilometers or 131,213 acres, measured from the chart polygon itself rather than quoted from anywhere. Add the next eight lakes on the list together and you still do not reach it. Upstream of it on the Fox the pack also carries Lake Poygan at 14,159 acres, Lake Winneshiek at 8,920 and Lake Butte des Morts at 8,550, so the whole pool is charted, not only the big open part of it.
Here are the eight largest named lakes in the pack.
Below those, Lake Koshkonong comes in at 10,527 acres, Lake Onalaska at 10,453, Lake Mendota at 9,736 and Green Lake at 9,341. The Madison water gives you a sense of the scale up north: Mendota would fit inside Petenwell twice over with room left. Lake Geneva at 5,387 acres closes out the twenty largest, and it is still bigger than most of the water people drive two hours to fish.
The packs are cut to a box, not to the state line, and border water is better for it. Lake Pepin has the line running down the middle of it and the pack carries all 25,304 acres, not the near half. Lake Saint Croix at 7,636 acres and Lake Onalaska at 10,453 work the same way on their own rivers. Lake Gogebic at 12,973 acres is in here because the box reaches past the line to the north, and it is in the Michigan pack as well.
So if the water you run is on a line, either pack shows it whole and you can pick on other grounds. Take the one that covers the rest of the season, the small lakes you fish midweek as well as the big trip, and the border lake comes along with it.
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 is 531.0 square kilometers, or 131,213 acres, measured from the chart polygon. That makes it the largest named lake the pack carries by a wide margin: add the next eight lakes on the list together and the total is still short of it. Second is Lake Pepin at 102.4 square kilometers, 25,304 acres, and third is Petenwell Lake at 92.5 square kilometers, 22,857 acres.
Real depth. Both flowages are in the pack, Petenwell at 22,857 acres and Castle Rock at 12,899, and inland depth comes from state elevation surveys rather than from NOAA charts, which do not chart a reservoir at all. The water body outlines come from the National Hydrography Dataset. Read the contours against whatever level the pool is being held at the day you go, since a flowage surface moves and a contour does not.
Both. The packs are cut to a box rather than to the state line, so water on a border lands in the packs on either side of it. All 25,304 acres of Pepin are in this pack, not just the eastern half. Lake Saint Croix at 7,636 acres, Lake Onalaska at 10,453 and Lake Gogebic at 12,973 all carry over the same way.
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