Tajo river · Tagus Basin · dam built in 1969 · latest official reading: 6 October 2026.
Alcántara II is currently at 55.8 % of capacity, about normal for the time of year. The week-41 average across 38 years of records is 58.0 %, a difference of −2.2 points.
For context: a year ago it stood at 70.7 % and a month ago at 63.8 %. Against last week’s reading it is falling fast (−2.1 points).
Blue line: average monthly filling across the whole record, from 1988. The dot marks today’s reading, 55.8 % in October.
With 2,023 weekly readings since 1988, the average pattern of Alcántara II is clear: it peaks in June at 74.6 % and bottoms out in November at 55.9 %. That 19-point range makes it a reservoir with a moderate annual swing.
The highest reading in the whole series is 99.3 %, on 10 June 2025, and the lowest 35.9 %, on 13 November 2007. Comparing today against those two extremes says more than the bare percentage: 50 % is good news in a pool that rarely tops 60 %, and bad news in one that is usually full.
At 3,160 hm³ of capacity it is the largest of the 51 dams the bulletin tracks in the Tagus basin, holding 28.6 % of the whole demarcation’s capacity on its own. The basin as a whole is at 54.2 % today, so this reservoir is running closely in line with the basin as a whole.
The bulletin classifies it as a hydropower reservoir. That matters when reading the percentage: these pools fill and empty with electricity demand rather than the irrigation calendar, so a sharp drop does not necessarily mean scarcity.
The figures on this page come from the official MITECO reservoir archive, the same database behind Spain’s weekly hydrological bulletin. The bulletin covers every mainland reservoir above 5 hm³ of capacity and is published every Tuesday with Monday’s reading.
The latest reading here is from 6 October 2026, and the comparison series starts in 1988. Nothing is estimated, interpolated or forecast: the percentage is stored volume divided by the usable capacity the bulletin itself assigns to the dam. Historical averages are computed over the same calendar week in every previous year, the only fair comparison in a system with such marked seasonality.
See the whole demarcation, with all 51 dams the bulletin tracks: Tagus Basin.
