Lake Powell Water Temperature
Lake Powell's surface temperature peaks at 78–82 °F in July and August and bottoms out in the mid-40s °F in winter. Swimming is comfortable from roughly mid-June through September. Below Glen Canyon Dam it's a different story — the river releases stay cold (typically 46–60 °F) because they're drawn from deep in the reservoir.
Typical surface temperature by month
Long-term typical ranges for open-water surface temperature (NPS visitor guidance and historical readings). Actual readings vary with weather, wind mixing, and location on the lake.
| Month | Surface temp | Swimming |
|---|---|---|
| January | 46–49 °F | Too cold |
| February | 45–48 °F | Too cold |
| March | 48–54 °F | Too cold |
| April | 54–62 °F | Wetsuit only |
| May | 62–68 °F | Brisk |
| June | 70–76 °F | Comfortable |
| July | 78–82 °F | Ideal |
| August | 78–82 °F | Ideal |
| September | 72–77 °F | Comfortable |
| October | 63–68 °F | Brisk |
| November | 54–60 °F | Wetsuit only |
| December | 48–52 °F | Too cold |
Below the dam: a cold-water warning
The Colorado River immediately below Glen Canyon Dam is dramatically colder than the lake surface, because releases are drawn from penstocks more than 200 feet down where the water stays cold all year. The USGS gage at Lees Ferry (09380000) typically reads 46–60 °F year-round. Anglers love it (it sustains the famous Lees Ferry trout fishery); swimmers should treat it as cold-shock territory even in August.
Water temperature also interacts with lake level: in low-water years the warm surface layer sits closer to the penstocks, which is one reason release temperatures get monitored closely. See today's elevation on the live tracker and the seasonal rise and fall on the water level chart.
Water Temperature FAQ
How warm is Lake Powell in summer?
Surface water peaks at roughly 78–82 °F in July and August — comparable to a swimming pool. June and September typically run in the low-to-mid 70s.
When is Lake Powell warm enough to swim?
Most swimmers find the lake comfortable from mid-June through September, when surface temperatures hold above about 70 °F. May and October are doable for the tolerant; the rest of the year calls for a wetsuit.
Why is the water below Glen Canyon Dam so cold?
Releases are drawn from penstocks deep in the reservoir, where water stays cold year-round. The Colorado River at Lees Ferry below the dam typically runs 46–60 °F even in mid-summer — a shock compared to the lake's 80 °F surface.
Does the water temperature vary around the lake?
Yes. Shallow bays, beaches, and side canyons warm several degrees above the main channel in summer, while the deep water near the dam stays cooler. Wind mixing after storms can also drop surface readings temporarily.
Updated July 1, 2026 · Elevation data: U.S. Bureau of Reclamation (USBR). Ramp status: National Park Service (NPS). Informational only — verify conditions with official sources.