The Reservoir
Essays on water-data transparency
Behind-the-scenes notes, methodology deep-dives, country case studies, and observations from building the world's first systematic ranking of reservoir-data openness.
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Introducing the Reservoir Transparency Index: H1 2026
The inaugural, semi-annual ranking of how openly countries publish their reservoir storage data. The H1 2026 edition evaluated 194 countries — and the median one scores F.
September 2026 Reservoir Levels in our 15 countries: 52% average — South Africa at 96%, Lake Powell at 21%
The 1,913 reservoirs we track with a current volume reading held 52.2% of capacity in early September 2026. That average is not a climate. South Africa is 95.8% full. Lake Powell is 20.5%. India closed the monsoon at 61% and is still 10 points behind last year. Spain is 64%; Cyprus is 39%. Norway's south is 46% while the north is 91%.
India Reservoir Levels, September 2026: 61% Full, Still 10 Points Behind Last Year
India's monitored reservoirs held 61% of capacity on 3–4 September 2026 — 144 km³ across 307 reservoirs — after rising from 22% in early July. On a like-for-like basket the country is 10 points behind 3 September 2025. Madhya Pradesh and Indira Sagar have recovered; the remaining hole is the Cauvery (KRS 54% against 97% last year, Lower Bhawani 17% against 100%), plus Bhakra at 61% against 90%.
Bhakra Dam Water Level, August 2026: 53.9% Full as BBMB Tells Punjab, Haryana and Rajasthan to Cut Draws
Bhakra was 53.9% full on 20 August 2026 — 3,356 MCM, about 118.5 TMC of live storage. That's the CWC bulletin. The next day BBMB told Punjab, Haryana and Rajasthan to stop overdrawing. The dam is still filling: it was 21.4% on 2 July. Last mid-August it was at 70%, and a week later they opened the floodgates. Pong is 61.9%. Together they hold 1,994 MCM less than a year ago.
When India's Monsoon Ends, the Number Stays. 57 Reservoirs Have Already Missed Their Window
On 13 August 2026 Lower Bhawani was 24.1% full — where it started the monsoon — and in our CWC history this dam typically falls after mid-August. Add each reservoir's typical mid-August to late-September change from 2023–25 to the current reading, and 57 of 133 still miss their own September/October normal by five points or more. Indira Sagar projects to 57% against a 94% October normal. Koyna, Ujjani and Almatti have already banked the year. Tamil Nadu still has the northeast monsoon; Rajasthan and the Narmada do not.
Karnataka Reservoir Levels, August 2026: 69.3% Full as Almatti Goes From 3% to 92%
Karnataka's 18 major reservoirs were 69.3% full in the CWC bulletin of 13 August 2026, up 55.3 points from 14.0% on 2 July. Almatti, the state's largest dam, went from 2.9% to 92.4%; Tungabhadra from 3.3% to 82.7%, of which 31 points arrived in a single week. Krishnaraja Sagar (KRS) is 56.2% against 98.6% a year ago. On 13 dams with both years, the state is 61.1% now against 86.0% on 14 August 2025. Dam-by-dam table with capacities in TMC and MCM.
Mediterranean Sea Hits 33°C, 1.15°C Above the 2024 Record. Spain's Reservoirs Are 66% Full
Spain's reservoirs were 66.2% full on 18 August 2026 — 37.1 of 56.5 km³, some 13 points above the August normal — as the Sa Dragonera buoy off Mallorca logged 33.02°C, 1.15°C above the 12 August 2024 record that preceded Storm Boris and the Valencia DANA. The Mediterranean supplied about 78% of that flood's moisture; this year's sea is hotter. The basins that would receive the rain are not where they were: Catalonia's internal reservoirs are at 80% against 28% on DANA day, the Segura at 54% against 15%, the Júcar at 56%. Tous, the lower-Júcar flood dam, is still only 24% full.
The 10 Biggest Movers in India's Reservoirs, Monsoon 2026: Rengali Up 2,475 hm3, Lower Bhawani Gains Nothing
Between mid-May and mid-August 2026, 88 of the 121 Indian reservoirs we track through the monsoon rose and 25 fell, adding a net 27.5 km3. But in a monsoon almost everything rises, so each reservoir is measured against what it normally does across the same three months — and 68 of the 93 with a usable baseline are running below their own normal, by an average of 11.0 points. Rengali in Odisha added 2,475 hm3, more than any reservoir in India, climbing from 14.2% to 76.8% after falling to empty in early July. Lower Bhawani in Tamil Nadu normally gains 72.5 points across this window and this year gained none, finishing at 24.1% against 100% a year ago. Bisalpur, which supplies Jaipur, sits at 68.7% against 98.4% last August. Ten reservoirs, a paragraph each, with volumes in hm3.
The 10 Biggest Movers in US Reservoirs, Summer 2026: Corpus Christi Up 80 Points, Jackson Lake Down 49
Between mid-May and mid-August 2026, 313 of the 449 US reservoirs we track fell and only 97 rose — a net loss of 18.6 km3 and a drop in weighted storage from 64.5% to 58.9%. Lake Corpus Christi in south Texas gained 80.3 points, from 11.2% to 91.5%, the highest reading in our four-year record and a level it reached from a low set the same spring. Jackson Lake in Wyoming gave up 49.4 points and 516 hm3 against a 69.3% August normal. American Falls in Idaho lost more water than any other reservoir, 1,090 hm3, yet drew down less steeply than it usually does. Every reservoir is measured twice: the raw 90-day move, and the same calendar window in prior years, so seasonal irrigation drawdowns are separated from genuine anomalies. Ten reservoirs, a paragraph each, with the volumes in hm3 and acre-feet.
Maharashtra Reservoir Levels, August 2026: 83.2% Full as the Ghats Dams Go From Empty to Overflowing
Maharashtra's 35 major reservoirs were 83.2% full in the CWC bulletin of 13 August 2026, up 64.7 points from 18.5% on 2 July — a complete reversal of the July picture. Koyna has gone from 10.9% to 96.8%, Mulshi from 9.6% to 95.5%, and Ujjani, the state's largest dam at 123.3 TMC, from dead storage to 95.0%. Marathwada's Jayakwadi is 95.1% full against a 51% August average. The state is 3.9 points ahead of last year on a like-for-like basis, against a national figure of 51.3%. Twenty-two of the 35 dams are above 90%; the laggards are Upper Wardha in Vidarbha (56.4% against a 78% average) and the Manjara sub-basin. Dam-by-dam table with capacities in TMC and MCM.
Lake Mead Water Level Today: 24.7% Full in August 2026, the Lowest in Five Years
Lake Mead was 24.7% full on 12 August 2026 — about 6.97 million acre-feet of its 28.26 maf capacity behind Hoover Dam, and the lowest reading in the five years of daily Bureau of Reclamation data we hold, below even the 25.1% of the 2022 crisis. The reservoir has fallen every month since peaking at 31.5% on 27 February, giving up roughly 1.92 million acre-feet in under six months and 1.04 million over the year. Its decline is slowing only because Lake Powell upstream is being drained more than twice as fast to hold it up: together the Colorado's two giants hold 23.0% of capacity, 12.25 million acre-feet of a possible 53.28.
Lake Powell Water Level Today: 21.1% Full in August 2026, 0.1 Points From Its Record Low
Lake Powell was 21.1% full on 12 August 2026 — about 5.28 million acre-feet of its 25.03 maf capacity behind Glen Canyon Dam, and just 0.1 percentage points above the lowest reading in our five-year record. The date that explains the year is 1 January: that was Powell's high-water mark for 2026. The entire spring snowmelt was worth 0.4 points, a single gain in May, in a reservoir built to capture the Rocky Mountain runoff. It has lost 7.9 points and about 1.99 million acre-feet in twelve months — more than twice the rate of Lake Mead downstream, because Powell is the reservoir being drained to hold Mead up.
Madhya Pradesh Reservoir Levels, August 2026: 40.9% Full as the Narmada Refills, Still 26 Points Behind Last Year
Madhya Pradesh's 12 major reservoirs were 40.9% full in the CWC bulletin of 6 August 2026, up 11 points in five weeks from 29.7% in early July — the monsoon has reached the Narmada catchment at last. Indira Sagar, the largest reservoir in India by capacity (431.6 TMC), has more than doubled to 31.5%, and Tawa rose 9.9 points in a single week to 23.5%. But the state was 67.4% full on the same week in 2025, so it is 26.5 points behind last year and about 32 points below its August average. The five Narmada-basin dams, 55% of the state's capacity, are only 26.9% full; Gandhi Sagar on the Chambal (62.3%) is the only major dam at its normal level and the only one ahead of last year. Dam-by-dam table with capacities in TMC and MCM.
