Nine decades of Lake Velence

Water level at the Agárd gauge on the Velencei-tó, 1934–2026 — one of the longest public records in the OVF archive. The lake nearly dried out in the 1930s, hit its recorded high in 1940 and crashed in the 2022 drought — and July 2026 is worse: 43 cm so far, twelve centimetres under the 2022 crisis floor and a level last seen in 1938. Retrieved by an AI agent through ovf-data-mcp. Operational data — preliminary, unchecked.

Yearly water level, 1934–2025 (cm, local gauge zero)

Line: yearly mean · band: yearly min–max · hover or focus + arrow keys for values

Monthly mean, January 2019 – July 2026 (cm)

The recent slide in close-up · last month is partial (to 17 Jul) · hover or focus + arrow keys for values

Data table — yearly, 1934–2025

Year	Mean (cm)	Min (cm)	Max (cm)

How this page was made

An agent found the gauge, inspected coverage (data back to 1934), then ran yearly server-side aggregations in date-bounded chunks plus a monthly close-up:

vizugy stations search Velence
vizugy observations coverage surface:818          # available from 1934-01-01
vizugy observations aggregate surface:818 --start 1934-01-01T00:00:00Z \
    --end 1960-01-01T00:00:00Z --interval yearly --operation avg   # × avg/min/max × 4 windows
vizugy observations aggregate surface:818 --start 2019-01-01T00:00:00Z \
    --end 2026-07-18T00:00:00Z --interval monthly --operation avg

These commands are the only data source. The agent then merged the JSON responses and wrote this page’s HTML, CSS, and JavaScript itself — no chart libraries, no build step.

Source: Országos Vízügyi Főigazgatóság (OVF) via the public VRAQuery API · station Agárd (818), Velencei-tó, metric “Felszíni vízállás” (surface water level, cm), data type “operatív összefésült” · retrieved 2026-07-18 10:49 (UTC). Levels are centimetres above local gauge zero; 2026 is a partial year — it appears as a detached “to date” marker in the yearly panel (not on the full-year line) and in the monthly panel. Aggregation buckets follow upstream hydrological/local-day boundaries (bucket labels shifted to local time here). Early-decade values predate modern regulation of the lake. Operational values may be preliminary; for checked data follow OVF’s formal data-request process.