The Colorado supplies roughly 40 million people and 5 million acres of farmland across seven U.S. states and Mexico. Follow it down the page: snowmelt gathers in the Upper Basin, tributaries join and widen the river through the canyons, then nearly every drop is drawn off — for farms, cities, lawns, pools and golf courses — or lost to evaporation, until only a trickle reaches the sea. About three of every four gallons go to agriculture.
The river runs down the center: it widens where a tributary joins (blue arrows in) and narrows as each use is drawn off (arrows out); a thin arrow curving back shows water returned to the river. Bars mark the dams. Reservoir totals and treaty deliveries are rounded long-term averages under the “Law of the River”; the split of each city’s water into lawns & pools, golf and indoor use is illustrative, to show how much urban water — especially in California — goes to outdoor, non-returning uses. MAF = million acre-feet per year. Hydropower is in-stream (it passes through the dams without being consumed). Actual deliveries vary year to year and have been cut under recent shortage guidelines.
Ranked by long-term average consumptive use — the MAF column is water actually consumed. Each bar’s full length is the withdrawal for that use: the solid part is consumed and the cross-hatched tail is returned to the river for someone downstream. Return fractions are illustrative; the contrast that matters is that indoor city water largely comes back while lawns, pools and golf courses consume nearly all of theirs. Agriculture’s split between livestock-feed crops (alfalfa and grass hay) and everything else follows published basin research; feed crops alone consume more of the Colorado than every city, lawn, golf course and factory in the basin combined. Data-center use is small today but is the fastest-growing category, and figures for it are estimates — most operators do not publish site-level water data. Excluding the Mexico treaty delivery and reservoir evaporation, farming accounts for roughly three-quarters of the water actually used in the U.S. portion of the basin.
Every dam on the diagram above is also a generator. Hydropower depends on two things — how much water moves through, and how far it falls — so a falling reservoir cuts output twice over: less water, and less pressure behind it. That makes these numbers a direct read-out of the levels on this page.
Nameplate capacity (MW) is the maximum a plant can produce at once; generation (GWh per year) is what it actually delivers over a year — one GWh powers about 95 average American homes for a year. Grid shares are against roughly 4.4 PWh — 4,400 TWh — of total U.S. net generation from all sources per year (EIA); together these dams are a small slice of the national grid but a critical one regionally, and they supply the fast-ramping power that helps balance it. Figures are long-term averages from Reclamation, WAPA and the operating utilities — actual output swings with runoff and reservoir elevation. Output at Glen Canyon and Hoover has fallen sharply since 2000 as Powell and Mead dropped: Glen Canyon has run roughly a third below its historical average in recent years, and at very low elevations a dam reaches “minimum power pool” and stops generating entirely, well before it reaches dead pool. The Salt River plants are operated for peaking and pumped storage, so they generate far less than their capacity suggests.