A day on Boysen Reservoir or Glendo Reservoir usually starts at a concrete ramp and turns into a wind that came up around two in the afternoon. Flaming Gorge Reservoir and Yellowstone Lake are a longer sort of day, with more open water between you and the far shore than people expect on the way out. Pathfinder Reservoir and Keyhole Reservoir are held water, and the line where the bank meets the water on those is not in the same place in September that it was in June. That moving line is the thing a chart of held water has to account for.
The Wyoming pack carries 3,736 charted water bodies. 1,804 of them are named, which puts it 14th of the 48 state lake packs for named water, ahead of where its total count sits at 23rd. 92 of the named lakes measure more than a square kilometer, and that figure is 26th of the 48. So the top of the list is short and the rest is small water: the pond at the end of a two track, the widening in a creek that still carries a name on the map.
The named count is the figure that stands out in this pack. 1,804 named water bodies is 14th of the 48 state lake packs, while the total of 3,736 is 23rd, so a larger share of the water in this box carries a name than in most packs. Close to half of it does. A name is what you use when somebody asks where you launched, and it is what tells one arm of a reservoir from the next one over.
The size ranking runs the other way. 92 named lakes over a square kilometer puts the pack 26th, the middle of the 48. Read the two numbers together and you have the shape of the water: a short list of big reservoirs and lakes, then a long tail of small named water. All of it is charted the same way, with the outline from the National Hydrography Dataset and depth from state elevation surveys.
| Lake | Charted surface area |
|---|---|
| Yellowstone Lake | 340 km² (83,966 acres) |
| Flaming Gorge Reservoir | 156 km² (38,647 acres) |
| Jackson Lake | 108 km² (26,663 acres) |
| Pathfinder Reservoir | 89 km² (21,992 acres) |
| Boysen Reservoir | 75 km² (18,607 acres) |
| Palisades Reservoir | 56 km² (13,813 acres) |
| Seminoe Reservoir | 56 km² (13,813 acres) |
| Bighorn Lake | 50 km² (12,331 acres) |
| Glendo Reservoir | 48 km² (11,985 acres) |
| Keyhole Reservoir | 36 km² (8,797 acres) |
| Fontenelle Reservoir | 32 km² (7,784 acres) |
| Shoshone Lake | 30 km² (7,512 acres) |
The twelve largest named lakes the Wyoming pack carries, by charted surface area, measured from the chart polygon itself. The pack carries 3,736 charted water bodies in all, 1,804 of them named, and 92 named lakes larger than one square kilometer.
There is no NOAA chart for a reservoir. Inland depth in Helm is built from state elevation surveys instead, and the water bodies themselves come from the National Hydrography Dataset. That is the reason a lake like Seminoe Reservoir is charted water in Helm rather than a blue shape with a name printed on it, and it is what lets a run across one be planned against the draft of your own boat.
It also changes how you read a contour on held water. A reservoir sits at whatever level it is being held at, and that level moves through the season and from one year to the next. The contour describes the shape of the bottom, which stays where it is. The pool decides how much water is standing over that shape on the morning you launch. The flat inside a cove on Pathfinder Reservoir is in the same place in September as it was in June with less over it, and the shape is the part worth studying the night before.
Yellowstone Lake is the largest water body in the pack at 339.8 square kilometers, or 83,966 acres. It covers more surface than Flaming Gorge Reservoir at 156.4 square kilometers (38,647 acres) and Jackson Lake at 107.9 (26,663) put together, which is worth knowing before you plan a crossing on the strength of having run one of those two.
Under them the drop is steady. Pathfinder Reservoir is 89.0 square kilometers (21,992 acres) and Boysen Reservoir 75.3 (18,607). Then two land on the same figure: Palisades Reservoir and Seminoe Reservoir both measure 55.9 square kilometers, 13,813 acres, taken off the chart polygon itself. Bighorn Lake is 49.9 (12,331) and Glendo Reservoir 48.5 (11,985). Those four sit close enough together that surface area is not what decides which one you trailer to.
Below the top of the list the sizes come down to something you can fish in an afternoon, and there is far more of it. These are the next ones, measured the same way off the chart polygon.
Fremont Lake at 20.3 square kilometers is a little over a quarter of Boysen Reservoir, which is not obvious standing on the bank of either one. Grayrocks Reservoir and Cooper Lake match each other to the tenth. The pack runs a long way past this list as well: 92 named lakes come in over a square kilometer and 1,804 carry a name at all, so most of what is charted here is smaller than anything above.
One thing about the pack boundary. The packs are cut to a box rather than to a state line, so a lake near a border is carried by more than one of them. If the water you run is up against the Montana or the Colorado side, take the neighboring pack down as well and the whole lake is on the device before you leave the house.
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.
Depth. The pack carries Flaming Gorge Reservoir at 156.4 square kilometers, or 38,647 acres, with the outline from the National Hydrography Dataset and depth built from state elevation surveys, so the water has contours and a reading on it. Enter your draft once and the water your boat cannot cross shades on the chart. The packs are cut to a box rather than to a state line, so if you run the far end of that reservoir it is worth taking the neighboring pack down too.
A little over three times the surface. The pack measures Yellowstone Lake at 339.8 square kilometers (83,966 acres) and Jackson Lake at 107.9 (26,663), both off the chart polygon. Yellowstone Lake is also larger than Jackson Lake and Flaming Gorge Reservoir added together, which is the figure to keep in mind when you are estimating how long a crossing takes at your cruising speed.
Yes, and a low pool is when it earns its keep. Inland depth comes from state elevation surveys of the bottom, so the contours describe a shape that does not move. What moves is the level the reservoir is being held at. The creek channel you ran in June is the same line in October, and with your draft entered the shoulders on either side shade while the channel stays open. Once the pack is on the device that shading works at the ramp with no bars on your phone.
Helm Boating