Jack Schmidt
Center for Colorado River Studies, Utah State University
14 July 2025
Water stored in the reservoirs of the Colorado River represents the account balance from which we draw water for use. The amount in the account is especially important during dry times when the demand by water users throughout the Basin exceeds income to the account, primarily snowmelt runoff, and is met by account withdrawals.
The annual cycle of reservoir hydrology includes two seasons – a relatively short season when reservoir storage increases and a relatively long season when storage decreases. In wet years, the season when storage increases typically begins in March or early April and may last until late July. In dry years, this season might not begin until May and end in mid-June. During the rest of the year, the Basin’s reservoirs are progressively depleted.
Snowmelt in 2025 was low, similar to what it was in 2012 and 2013; in early June, the Colorado Basin River Forecast Center predicted that this year’s unregulated snowmelt inflow to Lake Powell will end up being 54% of the recent 30-yr average. In the 21st century, only 2002, 2018, and 2021 had lower inflows to Powell. Not surprisingly, the amount of water that accumulated in the Basin’s reservoirs during the 2025 snowmelt season was also unusually low. There are a few ways to consider the Basin’s reservoirs. We can consider every reservoir for which data are readily available[1]; we can consider the major reservoirs actively managed by Reclamation[2]; or, we can consider just Lake Powell and Lake Mead (hereafter, Powell+Mead). Considering only Lake Powell or only Lake Mead doesn’t tell us much, because all of the Rocky Mountain snowmelt is first stored in Lake Powell and subsequently transferred to Lake Mead. In 2025, the 46 Basin reservoirs gained only 0.55 million af (acre feet) of water, of which only 0.28 million af accumulated in the 12 federal reservoirs and only 0.11 million af accumulated in Powell+Mead. That is a very small amount, especially compared to 2023 and 2024 (Fig. 1). That accumulation is being quickly consumed. By 1 July 2025, all of the 2025 accumulation in Powell+Mead had been released downstream or evaporated.

Figure 1. Graph showing reservoir storage in different parts of the Colorado River Basin since 1 January 2023. Total storage in March 2023 was the lowest in the 21st century. Storage significantly increased due to 2023 snowmelt, but the accumulation from the 2024 snowmelt was entirely lost. This will also happen in the coming months. On 30 June 2025, active storage in 42 reservoirs upstream from Lake Powell was 8.58 million af, active storage in Lake Mead was 8.05 million af, and storage in Lake Powell was 7.88 million af.
In contrast to previous dry years, however, today’s account balance is unusually low, about the same as in late July 2021 (Fig. 2). Depending on how you think about the reservoir system, today’s contents are between 34 and 45% full in relation to their condition at the beginning of the 21st century (Table 1).

Figure 2. Graph showing reservoir storage in different parts of the Colorado River Basin since 1 January 1999. On 30 June 2025, total basin storage was comparable to what it was in late July 2021
Table 1. Present storage contents of reservoirs in the Colorado River Basin in relation to past conditions.
Storage contents, in million acre feet | |||
on 30 June 2025 | Last time storage was as low | Present storage as a percentage of storage in late July 1999 | |
entire Basin (n=46) | 26.8 | 25-Jul-21 | 45% |
federal reservoirs (n=12) | 23.64 | 4-Sep-21 | 42% |
Powell + Mead | 15.93 | 20-Nov-21 | 34% |
The implications for Lake Powell depend on whether Reclamation decides to emphasize water storage in Lake Powell or in Lake Mead, and whether water presently in Flaming Gorge reservoir will be released to supplement storage in Lake Powell. As of June 30, 32% of the reservoir storage in the Basin was in 42 reservoirs upstream from Powell, 30% was in Mead, and 29% was in Powell (Fig. 1). if past management practices prevail, storage upstream from Powell will be quickly reduced, and storage in Powell and Mead will be reduced more slowly. If Reclamation emphasizes storage in Lake Powell by reducing releases to Lake Mead through the Grand Canyon, hydropower production at Glen Canyon Dam will be maintained and the risk of entrainment of smallmouth bass through the turbines will be reduced. But this management approach will cause Lake Mead to fall more quickl, thereby reducing hydropower production at Hoover Dam and perhaps the quality of water withdrawn to southern Nevada. Water storage can’t be maximized in both reservoirs at the same time. Indeed, we are living in dry times!
[1] There are 46, https://www.usbr.gov/uc/water/hydrodata/reservoir_data/site_map.html.
[2] There are 12 included in Reclamation’s monthly 12-month study reports (Taylor Park, Blue Mesa, Morrow Point, Crystal, Fontenelle, Flaming Gorge, Navajo, Vallecito, Lake Powell, Lake Mead, Lake Mohave, and Lake Havasu).