Lithuania Reservoir Transparency

LHMT publishes water level readings (in centimetres above gauge zero) for two stations on the Kaunas Reservoir (Kauno marios — Darsūniškio VMS and Birštono VMS) and for the Nemunas at Kaunas, all accessible via meteo.lt. A Šventoji-basin gauge intermittently reflects Antalieptė reservoir level. However, no volumetric storage data (Mm³ or % fill) is published for the Kaunas Lagoon or any other reservoir. The Kruonis Pumped Storage upper basin (48 Mm³) has no public data at all. Storage must be inferred from stage-volume curves not provided to the public. The absence of any direct storage-volume metric for the covered subset is the primary constraint.

A REST JSON API (api.meteo.lt) launched in November 2023 provides no-registration, openly-licensed access to 30 days of hourly water level and temperature data from 95 hydro stations, including the two Kaunas Reservoir stations and the Šventoji gauges. Endpoints follow a logical structure (/hydro-stations/{code}/observations/measured/{date}) and historical annual data is reportedly available from the year 2000 via separate endpoints. The main limitation is that API documentation is in Lithuanian only, creating a friction barrier for international users. Data is in JSON (open format). No download restriction or paywall.

Conservative capacity-weighted estimate applied 2026-05-29. Numerator/denominator: n_covered ≈ 400 / n_total ≈ 880 hm³ across 5 reservoirs above 10 hm³: Kaunas Lagoon/Kauno marios (~460 hm³ on the Nemunas), Antalieptė reservoir on the Šventoji (~80 hm³), Kruonis Pumped Storage upper basin (~48 hm³), Angiriai on the Šušvė (~16 hm³), Bubiai near Šiauliai (~12 hm³). LHMT api.meteo.lt covers Kaunas (2 gauges) and a Šventoji gauge adjacent to Antalieptė. Applying conservative downward adjustment (~-7 points) to recognise that (1) the Kaunas Lagoon publication is gauge-level only, not the full ~460 hm³ volumetric storage, (2) the Šventoji gauge is adjacent to rather than measuring Antalieptė directly, and (3) Kruonis PSP upper basin, Bubiai and Angiriai have no public station at all. coverage = round(100 × 400 / 880) = 45.

Scoped to the 2 covered reservoirs, the LHMT API documentation indicates annual historical hydrological data is available from the year 2000 onward via api.meteo.lt endpoints, with previous-year data typically published from mid-current year. Hydrological yearbooks in PDF are available for 2016–2018, 2019–2021, and 2022 (~10 years), providing multi-year station-level summaries. The API's rolling near-real-time window is 30 days, but the underlying long-term archive (since 2000, ~25 years) appears queryable. The median historical depth across the 2 covered reservoirs is approximately 20 years. The constraint is that archive access for hydrological data has not been explicitly confirmed to be as deep as the meteorological archive, and yearbooks are PDF-only.

Automatic water measurement stations at the 2 covered reservoirs record water level every 15 minutes using SEBA Hydrometrie equipment. The LHMT API exposes this as hourly aggregated observations, freely accessible without delay. The meteo.lt web interface shows current hydrological network data labelled as operational (pre-reliability-assessment). Temperature data for regional parks updates weekly (every Thursday), but water level at the main hydro stations is effectively near real-time. The update cadence for the Kaunas reservoir gauge stations matches or exceeds most EU peers for water level proxies.

The LHMT operates under ISO 9001:2015 quality management and its Metrology Laboratory holds ISO/IEC 17025:2018 and ISO/IEC 17020:2012 accreditation. The measurement datum (gauge zero, set approximately 0.5 m below the minimum observed water level) is publicly described on meteo.lt. Equipment type (SEBA Hydrometrie automatic stations, 15-minute intervals) is referenced in published scientific literature. However, no consolidated public methodology document covering stage-volume conversion, data quality procedures, or gap-filling protocols exists in an accessible online format for the covered reservoirs. The institutional quality certifications are documented but the operational measurement methodology is not formally published for public review.

The meteo.lt website has a functioning English-language section that includes the hydrological information page and current water level/temperature data, making basic data inspection possible without Lithuanian. However, the API documentation at api.meteo.lt is entirely in Lithuanian, creating a significant barrier for programmatic access by non-Lithuanian users. Hydrological yearbooks are published in Lithuanian only. The ENTSO-E Transparency Platform provides some English-language weekly hydro energy data for Litgrid but this covers aggregated energy storage (MWh), not reservoir water volumes. Overall, English usability is partial: browse-level access is possible but technical integration requires Lithuanian-language navigation.