# Does rain raise the Lake Mead water level? > Barely. An inch of rain landing on Lake Mead adds about an inch to its surface, while the level itself is set by Colorado River water released from Lake Powell upstream and by what Hoover Dam lets out below. _Updated Oct 12, 2026._ Rain barely moves the Lake Mead water level. An inch of rain landing on the lake adds about an inch to its surface, and runoff from the surrounding desert adds a little more for a day or two, but an ordinary week of dam operations moves the lake by more than that. The level is set upstream and downstream rather than overhead: by how much Colorado River water Reclamation releases from Lake Powell at Glen Canyon Dam, and by how much Hoover Dam lets out below the lake. [Chart: Lake Mead storage](https://the-waterline.com/reservoir/lake-mead) ([data](https://the-waterline.com/reservoir/lake-mead.md) — chart image: https://the-waterline.com/charts/reservoir/lake-mead/chart.png) The latest reading is 1,037.53 feet above sea level on Oct 15, 2026, with 6.81M af in storage. ## Where Lake Mead's water comes from Most of the water in Lake Mead is Rocky Mountain snowmelt and runoff, as the Water Education Foundation puts it, and the main stem of the Colorado reaches the lake only after passing through Lake Powell and Glen Canyon Dam. What arrives is a release schedule, not a storm. Reclamation set Lake Powell's release for water year 2026 at 6.0 million acre-feet under the Mid-Elevation Release Tier, and the USGS gage on the [Colorado River at Lees Ferry](/streamflow/colorado-river-at-lees-ferry), just below the dam, measured about 5.8 million acre-feet between Oct 1, 2025 and Sep 23, 2026. Local water does get in. The Southern Nevada Water Authority returns the Las Vegas Valley's treated wastewater to the lake through the Las Vegas Wash, and storm runoff from the desert around the lake drains into it too. Neither is on the scale of the river. What leaves goes out through Hoover Dam. Those releases flow downstream into [Lake Mohave](/reservoir/lake-mohave), the reservoir behind Davis Dam, and on to Lake Havasu, where the Central Arizona Project and Southern California's Colorado River Aqueduct draw their supply. ## An inch of rain, in acre-feet Rain falling on a lake raises it by the depth of the rain, so the real question is how much water that depth holds. The site's own readings answer it. Between Aug 24 and Sep 23, 2026, Lake Mead lost about 68,400 acre-feet of storage for every foot its surface fell. That ratio is the lake's surface area at its September 2026 level: about 68,400 acres, well under half the 162,700 acres it covers at full pool. Worked example: an inch of rain over 68,400 acres is 68,400 ÷ 12, or about 5,700 acre-feet. The Colorado at Lees Ferry ran 8,070 cfs on Sep 23, 2026. One cfs sustained for a day is about 1.98 acre-feet, so the river was carrying about 16,000 acre-feet a day, and that whole inch of rain equals roughly eight and a half hours of it. Over a whole year the gap is wider still. The National Weather Service's 1991-2020 normal for Las Vegas is 4.18 inches of precipitation a year. The US Geological Survey measured average evaporation off Lake Mead of 6.22 feet a year, about 75 inches, between May 2013 and April 2019. Rain falling straight onto the lake puts back roughly one eighteenth of what evaporation takes off it. ## What a big storm looked like Tropical Storm Hilary is the best recent test. The National Hurricane Center reported 2 to 4 inches of rain over southern Nevada in August 2023, with 9.20 inches at Lee Canyon in the Spring Mountains. In the week of Aug 18 to Aug 25, 2023, Lake Mead rose 1.09 feet. It had risen between 0.71 and 1.34 feet in each of the six weeks before the storm, so the storm week landed inside the range the lake was already running at. The river was doing the lifting that summer: Lees Ferry averaged 16,844 cfs in July and August 2023, against 11,343 cfs in the same two months of 2022. The four largest one-day rises of the past five years came from a dam. Lake Mead rose 0.41, 0.74, 0.75 and 0.53 feet on Apr 26 through Apr 29, 2023, as the water from a High-Flow Experiment arrived. For that experiment Reclamation released about 39,500 cfs from Glen Canyon Dam for 72 hours starting Apr 24, according to the National Park Service. ## Lake Mead water level before and after The same arithmetic explains the before-and-after photos. Lake Mead stood at 1,040.58 feet above sea level on Jul 28, 2022, the low of that drought. Larger releases from Powell carried it to 1,076.62 feet by Mar 4, 2024, a 36-foot rise with no change in how much rain falls on southern Nevada. By Sep 23, 2026 the surface was back down to 1,038.06 feet, below the 2022 low, in a water year when Reclamation set the release from Powell at 6.0 million acre-feet. The readings that move the lake are upstream: [Lake Powell](/reservoir/lake-powell), the [Colorado River at Lees Ferry](/streamflow/colorado-river-at-lees-ferry) and the [Upper Colorado River Basin snowpack](/snowpack/upper-colorado-river-basin). [Lake Mead water level](/reservoir/lake-mead) carries the daily reading in feet and acre-feet, and [Lake Mead water level by year](/guides/lake-mead-water-level-history) has the level at the end of every year since 1935. ## Related data + guides - [Lake Mead water level](https://the-waterline.com/reservoir/lake-mead) - [Lake Powell water level](https://the-waterline.com/reservoir/lake-powell) - [Colorado River at Lees Ferry](https://the-waterline.com/streamflow/colorado-river-at-lees-ferry) - [The Colorado River system in charts](https://the-waterline.com/guides/the-colorado-river-system-in-charts) - [Lake Mohave water level](https://the-waterline.com/reservoir/lake-mohave) - [Lake Mead water level by year](https://the-waterline.com/guides/lake-mead-water-level-history) ## Common questions ### Does rain raise the Lake Mead water level? Only slightly. An inch of rain landing on the lake adds about an inch to its surface. At the lake's size in September 2026, about 68,400 acres, that is roughly 5,700 acre-feet, which the Colorado River delivered in about eight and a half hours at the flow measured at Lees Ferry on Sep 23, 2026. ### Why is Lake Mead still low after a big storm? Because the storm is local and the lake's supply is not. Most of Lake Mead's water arrives down the Colorado River from Lake Powell on a release schedule Reclamation sets each water year, and evaporation removes about 6.2 feet of water a year from the surface, per USGS. ### How much water does Lake Mead lose to evaporation? USGS measured an average of 6.22 feet a year off Lake Mead's surface between May 2013 and April 2019. At the lake's September 2026 surface area of about 68,400 acres, that rate works out to roughly 425,000 acre-feet a year. ### What raises the Lake Mead water level the most? Water released from Glen Canyon Dam upstream. The four largest one-day rises of the past five years came in late April 2023, when a High-Flow Experiment sent about 39,500 cfs down the river for 72 hours. ### Where can I see the Lake Mead water level today? [Lake Mead water level](/reservoir/lake-mead) updates daily with Reclamation's reading in feet above sea level and in acre-feet of storage, compared to the lake's five-year median for the date. --- Canonical URL: https://the-waterline.com/guides/why-rain-rarely-changes-lake-mead-level