Slovakia Reservoir Transparency

Slovakia's reservoir data landscape is split across two partly overlapping institutional silos. SEPS (transmission system operator) publishes the filling rate of hydropower-connected water reservoirs daily since August 2010, accessible via its Damas Energy portal (dae.sepsas.sk). SHMÚ publishes real-time water levels at ~400 gauging stations and seasonal water temperatures for 12 named reservoirs, but does NOT publish storage volumes or fill percentages. SVP, which manages 46 large and 255 smaller reservoirs, does not publish any operational storage data to the public — its website redirects users to SHMÚ for hydrological data. The SEPS dataset covers only the hydroelectrically active subset of reservoirs, leaving drinking-water and multi-purpose reservoirs (e.g., Starina, Zemplínska Šírava, Nosice) with no publicly available fill percentage data. Overall, partial coverage of the most volumetrically significant reservoirs is achieved, but the national picture is incomplete.

The SEPS Damas Energy platform provides a SOAP-based web service API (TLS 1.2, XML format) for registered market participants, but there is no public documented REST API for reservoir data. The public-facing reservoir filling information is viewable through an interactive web portal (dae.sepsas.sk), but no documented bulk download or machine-readable endpoint is available without registration. SHMÚ operates an opendata.shmu.sk portal with a rate-limited REST API for meteorological and river-level data, but this does not include reservoir storage volumes. The Modrá platforma (mpl.his.shmu.sk), which is intended to centralise hydrological data services, has its 'Data Services' section explicitly marked as 'in preparation' as of 2026. The overall programmatic accessibility for reservoir-specific storage data remains very low by international standards.

Conservative capacity-weighted estimate applied 2026-05-29. Numerator/denominator: n_covered ≈ 1,080 / n_total ≈ 1,500 hm³ across SVP's 46 large reservoirs. SHMÚ covers strategic reservoirs at the hydrometric-network level and SEPS publishes daily filling rates for hydropower-active reservoirs covering Liptovská Mara, Orava and the major Váh cascade. Applying conservative downward adjustment (~-8 points) to recognise that smaller industrial-use and privately operated reservoirs within SVP's portfolio are not in the SEPS or SHMÚ data feeds, drinking-water reservoirs (Starina, parts of Domaša) lack public fill data, and the 255 smaller SVP reservoirs below 10 hm³ are unaffected by the threshold but signal the broader institutional under-publication. coverage = round(100 × 1,080 / 1,500) = 72. The covered subset still captures the dominant Váh-cascade hydropower storage but the strategic-only nature of SEPS's mandate creates real gaps.

The SEPS Damas Energy portal explicitly states that reservoir filling rate data has been published daily since August 2010, providing approximately 16 years of continuous daily records as of 2026. This is a meaningful historical series by European standards. The ENTSO-E Transparency Platform also carries Slovakia's aggregate hydro storage data from around 2015 onwards (~11 years). SHMÚ river-level stations have records going back decades, but these are for river gauging, not reservoir storage. There is no known publicly accessible portal with reservoir fill percentages predating 2010 for Slovakia. Historical access to the SEPS data through the Damas Energy portal requires registration, which may limit practical retrieval.

SEPS publishes the reservoir filling rate daily (the page explicitly states 'published daily from August 2010'), which represents good operational frequency. The Damas Energy platform also offers 15-minute measured operational data for power system indicators, though it is unclear whether the reservoir filling component is updated at that granularity or only at a daily resolution. SHMÚ updates river-level gauging station readings at least daily (timestamps observed at 08:00 local time) and reservoir temperature twice weekly (Monday and Thursday, May–October). The ENTSO-E aggregate is weekly. Overall the daily update cadence from SEPS is appropriate for operational use.

Slovakia's institutional framework for water monitoring is described at a high level on SHMÚ and SVP websites, but no public document clearly explains how reservoir storage volumes are calculated, what bathymetric surveys underpin the capacity figures, or how filling percentages are derived. The SEPS operational data pages do not accompany reservoir filling figures with capacity baselines or measurement methodology. SHMÚ's water monitoring methodology (per the Water Framework Directive) is referenced in general terms on vuvh.sk and in the Water Plan of the Slovak Republic, but reservoir-specific capacity measurement protocols are not published in accessible English or Slovak documentation. The TELEDAN joint hydrology service (SVP/SHMÚ/VV) has a website but it returned certificate errors and its English-language documentation was inaccessible. Capacity figures cited publicly (e.g., Liptovská Mara 360 Mm³, Orava 346 Mm³) appear in Wikipedia and tourism sources but not in a consolidated official technical registry accessible to the public.

SEPS operates an English-language version of its website (sepsas.sk/en/) and the reservoir filling rate page is available in English, providing a basic entry point. However, the actual Damas Energy data portal (dae.sepsas.sk) defaults to Slovak and registration documentation is primarily in Slovak. The SHMÚ water monitoring interfaces and the Modrá platforma are exclusively in Slovak. SVP's English site exists but contains no operational data. ENTSO-E Transparency is fully in English and represents the only internationally accessible English-language view of Slovakia's aggregate hydro storage. Overall, English access is limited to high-level portal descriptions and the ENTSO-E aggregate; granular data requires navigating Slovak-only interfaces.