Seventeen of the twenty largest named lakes this pack carries have the word Reservoir in the name. Navajo Reservoir, John Martin Reservoir, Blue Mesa Reservoir and McPhee Reservoir are all held water, and so are most of the smaller ones people trailer to on a Saturday. Lake Granby, Lake Meredith and Twin Lakes are the three in that top twenty without the word on them. Boating held water has its own habits. You learn where the old creek channel runs, you learn which ramp stays usable when the pool comes down, and you read a shoreline that was underwater the last time you were out.
The pack carries 3,348 charted water bodies. Of those, 1,850 are named, and 129 of the named lakes are larger than a square kilometer. Among the 48 state lake packs that is thirteenth for named water and eighteenth for lakes over a square kilometer. The largest the pack carries is Navajo Reservoir, 61.9 square kilometers, or 15,296 acres, measured from the chart polygon itself.
For sheer count of water bodies the pack lands twenty-sixth of the 48, the middle of the field. For named water it lands thirteenth. More than half of everything in it carries a name, and the name is the part that matters when you are looking for one particular reservoir rather than admiring a total.
The 129 named lakes over a square kilometer are the ones you would actually put a boat on. Twin Lakes closes out the twenty largest at 8.3 square kilometers, or 2,051 acres, which leaves another 109 named lakes over a square kilometer sitting below it. Those are the Tuesday evening lakes, one ramp and a gravel lot, and they are charted the same way the big ones are.
| Lake | Charted surface area |
|---|---|
| Navajo Reservoir | 62 km² (15,296 acres) |
| John Martin Reservoir | 47 km² (11,639 acres) |
| Blue Mesa Reservoir | 36 km² (8,896 acres) |
| Lake Granby | 28 km² (7,042 acres) |
| Lake Meredith | 22 km² (5,510 acres) |
| Adobe Creek Reservoir | 19 km² (4,744 acres) |
| McPhee Reservoir | 18 km² (4,324 acres) |
| Riverside Reservoir | 15 km² (3,608 acres) |
| Dillon Reservoir | 13 km² (3,212 acres) |
| Neenoshe Reservoir | 13 km² (3,163 acres) |
| Elevenmile Canyon Reservoir | 12 km² (3,089 acres) |
| Horse Creek Reservoir | 12 km² (2,866 acres) |
The twelve largest named lakes the Colorado pack carries, by charted surface area, measured from the chart polygon itself. The pack carries 3,348 charted water bodies in all, 1,850 of them named, and 129 named lakes larger than one square kilometer.
NOAA charts the coast, the intracoastal and navigable rivers. A reservoir held behind a dam is none of those, which is why so much software shows one as a flat blue shape with a name floating in the middle of it. Helm builds inland depth from state elevation surveys instead, and takes the water bodies themselves from the National Hydrography Dataset. That pairing is what turns the shape into water you can plan a route across against your own draft.
A reservoir also sits at whatever level it is being held at that month. The bottom does not move. The surface over it does, held where the operators want it for irrigation, for storage, for whatever the year has been like. So a contour on this kind of water is worth reading as shape before you read it as a number: where the old creek channel runs, and where the flat at the mouth of a cove starts. That shape is the same in June and in September, and it is the thing you want in your head before you idle in past the buoys.
Navajo Reservoir at 61.9 square kilometers is larger than Dillon, Pueblo, Spinney Mountain and Twin Lakes put together, and it runs roughly a third larger than John Martin Reservoir behind it. Below the top three the sizes bunch up quickly. Lake Granby at 7,042 acres and Lake Meredith at 5,510 acres are closer to each other than either one is to Blue Mesa Reservoir at 8,896 acres, and by the time you reach Empire Reservoir in fifteenth place the gaps between neighbors are a couple of hundred acres.
These are areas taken off the chart polygon, so they describe the water the pack draws rather than a figure quoted from a brochure. Acres are the second number on each line for anyone used to reading them that way.
The measure tool is the one to use the night before. Draw a line from the ramp across to the far arm and you get distance, bearing and a depth profile along it, with the shallowest point marked rather than averaged in. On a reservoir with one long narrow arm, that single line is usually enough to tell you whether to run the middle or stay on the deep side.
Enter your draft once and it stays on the chart, shading the water your boat cannot cross and keeping routes off it. Download the pack at home on wifi and the charts, the depth shading, routing, the measure tool and the anchor alarm all keep working with no bars at the ramp. Helm puts the chart on the vehicle screen over CarPlay as well, which earns its keep on the tow to water you have only seen on a map. Saved spots and the logbook sync across devices, so a mark dropped from the phone in September is on the iPad next spring.
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. Navajo Reservoir is the largest named lake the pack carries, 61.9 square kilometers or 15,296 acres, and the contours on it are built from state elevation surveys while the water body itself comes from the National Hydrography Dataset. Enter your draft and the water your boat cannot cross shades on the chart. Draw a line across it with the measure tool and you get the shallowest point along that line rather than an average of it.
Blue Mesa. Measured off the chart polygon, Blue Mesa Reservoir is 36.0 square kilometers, or 8,896 acres, and Lake Granby is 28.5 square kilometers, or 7,042 acres. Both sit behind John Martin Reservoir at 11,639 acres and Navajo Reservoir at 15,296 acres, the two largest in the pack. Lake Meredith at 5,510 acres is the next one down after Granby.
The lake packs are cut to a box rather than to the state line, so water near a line comes along with the packs on both sides of it and can sit in two. Take the Colorado pack for the reservoirs you run most, and add the Wyoming, Nebraska, Kansas or Oklahoma pack if you tow across regularly. Each one works offline once it is on the device, so there is no penalty for keeping two of them aboard.
Helm Boating