JFRCalifornia
Keeper of San Juan Secrets
By the summer of 1966, Lake Powell had been filling for three years, but despite the initial optimism, the results were disappointing to the Bureau. The new reservoir was still struggling to rise. Any hope for the reservoir to be filled by 1970—the original best guess—was fading fast. Both 1963 and 1964 were below average runoff years, and only a deliberate effort to choke off flows through Glen Canyon Dam to a paltry 1,000 cfs in the spring and summer of 1964 allowed the lake to rise to minimum power pool, just over 3490. But a relatively healthy 1965 saw the lake finally rise at the rate it had been originally hoped for. By the late spring of 1966, Lake Powell reached 3545, its high point to date.
Any optimism that water managers at the Bureau may have had was soon dashed by what turned out to be yet another uncertain winter as 1966 turned to 1967. The timing of the new reservoir seemed poor. Out of the first 5 years of its existence, 4 were below average years, with the natural flow of the Colorado River producing 12 maf or less in all but 1965, hardly enough to sustain the needs of the users of the river, let alone allow for the rise of Lake Powell. But the ace up the sleeve at that time was that Lake Mead held a robust 15 maf, which allowed for the Bureau to minimize flows through Glen Canyon Dam as needed, at least until stronger runoff years returned.
The winter of 1966-67 saw Lake Powell drop, and quickly. It was the first winter that the Bureau could really see the effect of low runoff while keeping outflows at a normal rate, typically in the neighborhood of 7-10,000 cfs. On New Years Day 1967, the lake had fallen over 25 feet since the previous summer, now down to 3517. It continued to fall as winter continued into spring. By late May 1967, Lake Powell had fallen to 3502, barely high enough to maintain power through Glen Canyon Dam. What does that look like? All you have to do is watch the opening 15 minutes of the original Planet of the Apes, which was filmed at Lake Powell in late May 1967, just as the reservoir reached its nadir. An early version of the bathtub ring is clearly visible in the film, showing what then was the high water mark of 3545 reached the previous summer.
The winter of 1966-67 looked promising. Long before most people had heard of the term “El Niño”, 1966 was a strong El Niño year. By modern measures, expectations should have been great. And yet that El Niño fizzled, with snowpack over the winter producing nothing more than average runoff conditions in the spring. Still, in its depleted condition, the lake began to rise sharply in June 1967. For a few days, inflow peaked at over 50,000 cfs, a solid if not spectacular flow. But soon enough the runoff was spent, and the lake topped out at only just over 3530 in late July. Any hope for a miracle rise would have to wait for some time in the future.
Now in 2026-27, could we be facing a similar scenario as what happened 60 years ago?
The BOR seems to think so. As was the case in 1966, we are anticipating a strong El Niño. But the Bureau’s latest 24-month forecast is not bullish on the runoff potential for the coming winter. In the end, it predicts the lake will peak at just over 3530 in July 2027, just as it did in July 1967. If anything, the Bureau is trying harder to hold back water from going through the dam more than it did in 1966. Outflows through GCD that year totaled 7.7 maf. This time, the Bureau is looking to minimize that to 6 to 7 maf. If they aim for the low end of that outflow range, Powell is predicted to peak at 3541 next spring. Either way, they remain cautious about the coming El Niño.
Is there any hope for optimism based on the aftermath of 1966-67? After all, Lake Powell did eventually rise and fill, although it took 13 more years to reach full pool. The natural flow of the river was just above average from 1968-71, although none were spectacular years. And yet, this was enough to see the reservoir reach 3600 by 1970. Could this happen again?
It’s certainly plausible. But there are several things about the late 1960s that are no longer true today, and this does not bode well for the present. For one, there is no longer any cushion in Lake Mead. In 1966, Lake Mead held over 15 maf, allowing plenty of flexibility in releases through Glen Canyon Dam, while still being able to meet downstream water and power deliveries. As of September 2026, Lake Mead holds less than 7 maf.
Then there is the question of water use. Surprisingly, water use in the lower basin today is nearly identical to what it was in 1966, in fact slightly lower. That year, total use among those states was about 6.2 maf, compared to just about 5.8 maf in 2025. Recent restrictions from the BOR will hold water use at that level or even lower. The difference is the upper basin. In 1966, upper basin use was about 2.8 maf. Today, it’s closer to 4-4.5 maf, and there is no restriction on that use coming from the recent directive from the federal government. The net effect is that compared to 1966, the states are consuming more than a million acre feet more each year than they did 60 years ago, and it’s solely because of increased use in the upper basin states. Unless that changes, Lake Powell is at a disadvantage compared to the past.
And then finally there is climate change. Call it what you want, the fact is that in the past quarter century or more, it’s been hotter and drier. Evaporation rates are higher, soils are drier, and the same snowpack that might have fallen 60 years ago does not result in the same runoff as it did then. Is this another million acre feet or so? Estimates vary.
Between the increased water use in the upper basin and drier and hotter conditions in the modern world, we are operating at a net disadvantage of about 2 maf or perhaps more each year compared to 1966. What this means is that if the natural flow of the river was 12 maf in 1966, to produce the same conditions on Lake Powell would require a natural flow of 14 maf. Or maybe more. That’s a tall order, and another obstacle to surmount as we enter the El Niño winter of 2026-27. Since 2000, the average natural flow of the river system has been 12.2 maf. For comparison, here’s what natural flow has been in the past:
1906-22 – 16.3 maf (formed the basis for the 1922 Compact)
1940-59 – 14.1 maf
1960-79 – 13.4 maf
1980-99 – 16.1 maf
2000-25 – 12.2 maf
If you want a rule of thumb of what it would take just to keep the river system (and storage) level, it goes like this:
Let’s say we reduced upper basin use by 1 maf—a 25% cut. Then we’d only need an average of 13 maf to keep the system in balance. How often has than happened since 2000? Ten times. Still not enough. What we need to do is to reduce the total draw to less than the 21st century natural flow of 12.2 maf. That means cutting another 2 maf out of the total water use budget. And that means big cuts to the upper basin and Mexico (call it a 25-30% reduction each from current use), and perhaps even a little more out of the lower basin than they already have done. Painful, but that’s what’s got to happen, otherwise, we’re just banking on hope. Hope is not a plan. Of course, the plan also needs to include how to replace that reduced use, either though conservation, modified ag practices or new supplies. Or all three. And figure out how to do that with minimal cost, physical disruption, environmental impacts, and effects on existing water rights. With the pain fairly distributed among all the states. A tall order. (And no, the BRC's massively costly, overreaching and unrealistic "Colorado River Abundance Act" is not the answer, although it has a lot of interesting ideas worth considering in a more surgically realistic plan.)
And yes, if the conditions change again, and if the natural flow returns to what it once was in the 1980s or even much of the 90s, we can talk. Until then, we have to work the problem.
Any optimism that water managers at the Bureau may have had was soon dashed by what turned out to be yet another uncertain winter as 1966 turned to 1967. The timing of the new reservoir seemed poor. Out of the first 5 years of its existence, 4 were below average years, with the natural flow of the Colorado River producing 12 maf or less in all but 1965, hardly enough to sustain the needs of the users of the river, let alone allow for the rise of Lake Powell. But the ace up the sleeve at that time was that Lake Mead held a robust 15 maf, which allowed for the Bureau to minimize flows through Glen Canyon Dam as needed, at least until stronger runoff years returned.
The winter of 1966-67 saw Lake Powell drop, and quickly. It was the first winter that the Bureau could really see the effect of low runoff while keeping outflows at a normal rate, typically in the neighborhood of 7-10,000 cfs. On New Years Day 1967, the lake had fallen over 25 feet since the previous summer, now down to 3517. It continued to fall as winter continued into spring. By late May 1967, Lake Powell had fallen to 3502, barely high enough to maintain power through Glen Canyon Dam. What does that look like? All you have to do is watch the opening 15 minutes of the original Planet of the Apes, which was filmed at Lake Powell in late May 1967, just as the reservoir reached its nadir. An early version of the bathtub ring is clearly visible in the film, showing what then was the high water mark of 3545 reached the previous summer.
The winter of 1966-67 looked promising. Long before most people had heard of the term “El Niño”, 1966 was a strong El Niño year. By modern measures, expectations should have been great. And yet that El Niño fizzled, with snowpack over the winter producing nothing more than average runoff conditions in the spring. Still, in its depleted condition, the lake began to rise sharply in June 1967. For a few days, inflow peaked at over 50,000 cfs, a solid if not spectacular flow. But soon enough the runoff was spent, and the lake topped out at only just over 3530 in late July. Any hope for a miracle rise would have to wait for some time in the future.
Now in 2026-27, could we be facing a similar scenario as what happened 60 years ago?
The BOR seems to think so. As was the case in 1966, we are anticipating a strong El Niño. But the Bureau’s latest 24-month forecast is not bullish on the runoff potential for the coming winter. In the end, it predicts the lake will peak at just over 3530 in July 2027, just as it did in July 1967. If anything, the Bureau is trying harder to hold back water from going through the dam more than it did in 1966. Outflows through GCD that year totaled 7.7 maf. This time, the Bureau is looking to minimize that to 6 to 7 maf. If they aim for the low end of that outflow range, Powell is predicted to peak at 3541 next spring. Either way, they remain cautious about the coming El Niño.
Is there any hope for optimism based on the aftermath of 1966-67? After all, Lake Powell did eventually rise and fill, although it took 13 more years to reach full pool. The natural flow of the river was just above average from 1968-71, although none were spectacular years. And yet, this was enough to see the reservoir reach 3600 by 1970. Could this happen again?
It’s certainly plausible. But there are several things about the late 1960s that are no longer true today, and this does not bode well for the present. For one, there is no longer any cushion in Lake Mead. In 1966, Lake Mead held over 15 maf, allowing plenty of flexibility in releases through Glen Canyon Dam, while still being able to meet downstream water and power deliveries. As of September 2026, Lake Mead holds less than 7 maf.
Then there is the question of water use. Surprisingly, water use in the lower basin today is nearly identical to what it was in 1966, in fact slightly lower. That year, total use among those states was about 6.2 maf, compared to just about 5.8 maf in 2025. Recent restrictions from the BOR will hold water use at that level or even lower. The difference is the upper basin. In 1966, upper basin use was about 2.8 maf. Today, it’s closer to 4-4.5 maf, and there is no restriction on that use coming from the recent directive from the federal government. The net effect is that compared to 1966, the states are consuming more than a million acre feet more each year than they did 60 years ago, and it’s solely because of increased use in the upper basin states. Unless that changes, Lake Powell is at a disadvantage compared to the past.
And then finally there is climate change. Call it what you want, the fact is that in the past quarter century or more, it’s been hotter and drier. Evaporation rates are higher, soils are drier, and the same snowpack that might have fallen 60 years ago does not result in the same runoff as it did then. Is this another million acre feet or so? Estimates vary.
Between the increased water use in the upper basin and drier and hotter conditions in the modern world, we are operating at a net disadvantage of about 2 maf or perhaps more each year compared to 1966. What this means is that if the natural flow of the river was 12 maf in 1966, to produce the same conditions on Lake Powell would require a natural flow of 14 maf. Or maybe more. That’s a tall order, and another obstacle to surmount as we enter the El Niño winter of 2026-27. Since 2000, the average natural flow of the river system has been 12.2 maf. For comparison, here’s what natural flow has been in the past:
1906-22 – 16.3 maf (formed the basis for the 1922 Compact)
1940-59 – 14.1 maf
1960-79 – 13.4 maf
1980-99 – 16.1 maf
2000-25 – 12.2 maf
If you want a rule of thumb of what it would take just to keep the river system (and storage) level, it goes like this:
- Collective use in the upper and lower basin and Mexico – 12-12.5 maf.
- Evaporation, percolation and seepage – 1-1.5 maf (?)
- So the draw on the river is about 13-14 maf.
Let’s say we reduced upper basin use by 1 maf—a 25% cut. Then we’d only need an average of 13 maf to keep the system in balance. How often has than happened since 2000? Ten times. Still not enough. What we need to do is to reduce the total draw to less than the 21st century natural flow of 12.2 maf. That means cutting another 2 maf out of the total water use budget. And that means big cuts to the upper basin and Mexico (call it a 25-30% reduction each from current use), and perhaps even a little more out of the lower basin than they already have done. Painful, but that’s what’s got to happen, otherwise, we’re just banking on hope. Hope is not a plan. Of course, the plan also needs to include how to replace that reduced use, either though conservation, modified ag practices or new supplies. Or all three. And figure out how to do that with minimal cost, physical disruption, environmental impacts, and effects on existing water rights. With the pain fairly distributed among all the states. A tall order. (And no, the BRC's massively costly, overreaching and unrealistic "Colorado River Abundance Act" is not the answer, although it has a lot of interesting ideas worth considering in a more surgically realistic plan.)
And yes, if the conditions change again, and if the natural flow returns to what it once was in the 1980s or even much of the 90s, we can talk. Until then, we have to work the problem.
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