New Zealand's hydro lakes are running close to record levels for late winter. As of the week of 27 July 2026, national hydro storage was 3,598 GWh — 39% above its 93-year average for the date and 96% of the way up the full 1927–2025 range, meaning storage was near the highest late-July level in 99 years of records. Lake Te Anau sat at 202.77 m, at the very top of its 201.5–202.7 m consented operating range, and Lake Pūkaki, the country's largest single store, at 531.42 m — 93% of its operating range and 94% of the way up its historical energy range. The South Island, which holds almost all of New Zealand's controllable storage, was at the top of its recorded range for the date. Because New Zealand reports its lakes as stored electricity rather than water, these are, in effect, the charge level of the country's largest battery. Live figures for every lake and island are on the New Zealand page.
Key takeaways
- New Zealand's hydro storage was near record for the date — 3,598 GWh nationally in the week of 27 July 2026, 39% above the 93-year seasonal norm and 96% of the way up the 1927–2025 range. Live data on the New Zealand page.
- The South Island was at the top of its recorded range. Its 3,086 GWh was 46% above normal for the date and, within the precision of the published chart, at the 1927–2025 maximum for late July. Almost all of the country's controllable storage sits there.
- The big southern lakes were at or near the top of their operating ranges. Te Anau at 202.77 m (the top of its 201.5–202.7 m range), Pūkaki at 531.42 m (93% of 518.0–532.5 m), Manapōuri at 178.10 m (72% of 176.8–178.6 m).
- New Zealand counts its water as energy. Storage is published in gigawatt-hours, not cubic metres, because the lakes exist to generate electricity — so a fill figure here is a share of storable power.
- Level and stored energy are two different measures of the same lake, with different denominators: metres against consented limits, GWh against 99 years of storage history. In late July they happened to agree closely for Pūkaki; they do not have to.
- The buffer was already shrinking two weeks later. By 10 August national storage was 3,185 GWh, +27% on the average and 74% up the range — still comfortable, but the gap to normal had narrowed by 12 points in a fortnight.
Where the data comes from
New Zealand does not publish a single official "percent full" for its hydro system. What it publishes, weekly, is stored energy in gigawatt-hours (GWh) — from Meridian Energy and NZX's Comparative Hydro Storage series — alongside lake levels in metres on Meridian's lake-levels page. reservoirs.earth mirrors both: the national and island storage against the 93-year average and the full 1927–2025 range, and, for the three tracked Meridian lakes, the water level against each lake's published operating range.
How we read it, in plain sight. The storage series is published as charts, not data tables — but the weekly PDF is a vector document, so the plotted lines are the data themselves. We read the figures from that geometry rather than estimating them off the picture, calibrate each chart on its own axis labels, and check the result by confirming that the two island totals still sum to the national figure (they close to within 0.3%). The lake levels in metres are traced from Meridian's per-lake graphs and calibrated against the two published consented-limit lines, which reproduces the level Meridian states to within about 0.1 m. One limit remains: the timeliest per-lake storage feed in New Zealand is behind a paid subscription, so this is a weekly, free-tier picture. How we source and age this data is on the methodology page, and New Zealand's openness is scored in the Reservoir Transparency Index.
The current picture (week of 27 July 2026)
| Store | Stored energy | vs 93-yr average | Position in 1927–2025 range | Lake level (operating range) |
|---|---|---|---|---|
| South Island | 3,086 GWh | +46% | at the top of the range | — |
| North Island | 523 GWh | +9% | 56% | — |
| Lake Pūkaki | 1,648 GWh | +49% | 94% | 531.42 m · 93% |
| Lake Te Anau | 291 GWh | +64% | 90% | 202.77 m · top of range |
| Lake Manapōuri | 137 GWh | +41% | 77% | 178.10 m · 72% |
| National | 3,598 GWh | +39% | 96% | — |
Every line in that table is above its seasonal average, and most are in the top decile of their 99-year history for the date — an unusually uniform picture. The standout is the South Island: at 3,086 GWh it sat at the ceiling of everything recorded since 1927 for late July. The single sub-plot is the North Island, only 9% above its average and barely past the midpoint of its range — a reminder that the two islands do not move together.
Why New Zealand measures its lakes in gigawatt-hours
Most countries report a reservoir as a share of its water capacity — how many cubic metres it holds against how many it can hold. New Zealand's public hydro figures work differently, and for a good reason: the country's grid is largely hydropower, and the big southern lakes exist first and foremost to generate electricity. So the regulator and generators report what actually matters to the power system — the energy the stored water can still produce — in gigawatt-hours.
That makes the number unusually meaningful: a percentage against the historical range is a share of storable electricity, the physical input behind winter power security. It also means there is no honest, official "100% full" to divide by — no single maintained capacity figure across all the lakes — which is why reservoirs.earth shows New Zealand storage against its 93-year average and its historical range, rather than as a capacity-based fill percentage.
Lake level vs stored energy: the same lake, two different numbers
Each lake page here carries two percentages, and they answer different questions. The level in metres is measured against the lake's consented operating range — the band the operator is allowed to work within, which for Manapōuri is only 1.8 m wide. The energy in GWh is measured against the 1927–2025 range of stored energy, 99 years of actual history. Different denominators, different meanings: one tells you where the lake sits between its legal limits, the other what the power system can still generate.
In late July the two happened to agree closely for Pūkaki — 93% of its metre range, 94% of its energy range — but that is a coincidence of a near-full lake, not a rule. They diverge because energy and level are not linear with each other: as a lake drops it loses volume and head, the height the water falls through the turbines, so stored energy falls faster than the level does. The last metre of level is worth more generation than the first. Watch it happen in the fortnight after this snapshot: Pūkaki's level fell about a metre, from 531.42 m to 530.44 m — 7 points of its metre range — while its stored energy fell 128 GWh, nearly 9 points of its energy range. The narrow band a lake is legally held in is not the same thing as the electricity inside it, which is why we publish both.
What an above-average winter start means for the grid
New Zealand's reservoir calendar is a winter-drawdown system: storage is pulled down through the colder months to a late-winter low, then refills on spring inflows and snowmelt. Entering the back half of winter near the top of the 99-year range means an unusually large buffer for a grid that leans on these lakes when demand peaks and the wind is calm.
We publish reservoir data, not price forecasts. But storage is the physical input the electricity market reads, and in late July it read exceptionally healthy. The number to watch through August and September is not the raw level but the gap to the seasonal norm — and that gap is doing what drawdown seasons do. By 10 August, national storage was down to 3,185 GWh: still +27% on the average, but 74% up the historical range rather than 96%, with the North Island slipping to 11% below its own average. A near-record buffer in late July is not a guarantee about September; it is a head start.
What these numbers do — and don't — tell you
- The unit is energy, not water. A New Zealand fill figure is a share of storable electricity, so it should not be compared directly with the volumetric percentages of, say, Spain or the United States.
- Level and energy answer different questions. For a specific lake, the metre reading is measured against consented limits and the GWh figure against 99 years of history. They can move apart — see Pūkaki.
- Timing changes the meaning. Above-average in late-winter drawdown is a good sign; the same figure at the spring peak would be ordinary. Watch the gap to the norm, not the raw number.
- These figures are read from a published chart, not a data table. They come from the chart's own vector geometry rather than an eyeball estimate, and the island totals are checked against the national figure, but New Zealand still publishes no machine-readable storage feed. Everything links back to its source on the New Zealand page.
Correction (14 August 2026). This article originally carried storage figures that were too low and range positions that were badly wrong: national storage as "3,400 GWh, +28% above average", the South Island at "+43%", Pūkaki at "1,570 GWh, +21%" and the North Island at "+24%". Those numbers were estimated by eye from Meridian's weekly chart. They have been replaced throughout with figures read from the chart's underlying vector geometry — 3,598 GWh and +39% nationally, +46% for the South Island, 1,648 GWh and +49% for Pūkaki, +9% for the North Island — and the position-in-range figures, which were the worst affected, now appear as their own column: nationally 96% of the 1927–2025 range for the date, not the 56% the site previously showed. The lake levels in metres have shifted by 0.1–0.2 m to the readings for 27 July itself. A section arguing that Pūkaki was "nearly full on level but only mid-range on energy" rested on the wrong energy figure and has been rewritten: the two measures agreed closely that week. The header graphic shows the lake levels as of publication on 29 July, when Manapōuri stood at 66% of its operating range rather than the 72% it held on 27 July. The underlying data for every week of 2026 has been rebuilt from the same source; see the New Zealand page.