Treatment plants
Wastewater treatment plants and polluters
- Treatment plants near the fishing districts
- 265
- Does not meet the requirements
- 7
- Overloaded (above 100%)
- 29
- Discharged nitrogen
- 1,136t/year
Wastewater treatment plants
Register of treatment plants near the fishing districts
- Treatment plants near the fishing districtstreatment plants within 2 km of the fishing district; problem = fails EU requirements or is overloaded above 100%
- 230treatment plants with no fault found
- 35treatment plants with a problem (7 fail EU requirements, 29 overloaded)
Municipal treatment plants return treated water to watercourses. When they are overloaded or fail the requirements of EU Directive 91/271/EEC, more nutrients (nitrogen, phosphorus) and organic matter, which reduce oxygen in the water, reach the watercourse. The list contains 265 treatment plants that we found within 2 km of the line of Slovak fishing districts; 255 of them have load data and 13 have data on discharged pollution.
The list is not complete: it does not include treatment plants far from the fishing districts or industrial polluters (the National Pollution Register was unavailable when the data were collected). The treatment plant need not lie upstream of the fishing district and we do not assess the watercourse at the plant, so it counts only weakly towards the district score.
- Cleanest water31 fishing districts with no failed standardFishing districts, watercourses and groundwater stations without pollution
- Surface water294 of 363 sites fail the standard (2025)Worst sites, most frequent indicators and river basins
- Groundwater171 of 758 stations with substances from human activity (2025)Measured nitrates and harmful substances, map and trends since 2017
Most overloaded treatment plants
Load above 100% of capacity
- COV Podbanskecapacity 1,243 PEnear the district: Belá č. 1a267%
- COV Gabcikovocapacity 2,000 PEnear the fishing district: Dunaj č. 3 – odpadový kanál VD, Dunaj č. 3 – prívodný kanál VD and others (1)235%
- COV Tatranska Kotlina BTH1capacity 35 PEnear the fishing district: Biela č. 1, Beliansky potok and others (1)197%
- COV Hrabusicecapacity 2,500 PEat the fishing district: Hornád č. 5c, Veľká Biela Voda (NP Slovak Paradise) and 2 more185%
- COV Veselecapacity 1,440 PEnear the fishing district: Chtelnička, Dudváh č. 4175%
- COV Horne Salibycapacity 3,100 PEnear the district: Dudváh č. 1151%
- COV Kezmarokcapacity 29,556 PEnear the fishing district: Poprad č. 6a, Poprad č. 6b and others (3)151%
- COV Liptovsky Mikulascapacity 126,400 PEnear the fishing district: Váh č.20, Jalovecký potok and others (3)142%
- COV Samorincapacity 15,000 PEnear the district: Dunaj č. 3 – zdrž VD (Hrušov – Čunovo)136%
- COV Vlcany – Nededcapacity 9,000 PEnear the district: Váh č. 2135%
- COV Hradokcapacity 2,082 PEnear the fishing district: Váh č. 7, Hrádocký potok and others (2)130%
- COV Jaslovske Bohunicecapacity 5,550 PEnear the fishing district: Blava č. 1, Blava č. 2128%
Load is the ratio of the pollution produced to the treatment plant's capacity in population equivalents (PE). Above 100% the treatment plant may discharge less well-treated water.
Treatment plants that fail EU requirements
Directive 91/271/EEC on urban wastewater treatment
- COV Tlmacecapacity 4,000 PE · mechanicaldoes not meet the requirements70% of capacity (2,783 of 4,000 PE)
Fails: BOD₅, COD
Stated cause: poor treatment performance, unsuitable design or capacity, obsolescence
Near the fishing districts: Hron č. 3, VN Veľké Kozmálovce, VN Tekov and 1 more
- COV Trsticecapacity 4,000 PE · mechanical, biological, nitrogen removaldoes not meet the requirements38% of capacity (1,529 of 4,000 PE)
Fails: BOD₅, COD
Stated cause: poor treatment performance, unsuitable design or capacity, obsolescence
Near the fishing districts: Malý Dunaj č. 3, Malý Dunaj č. 2
- COV Zavadka nad Hronomcapacity 2,500 PE · mechanical, biological, nitrogen removaldoes not meet the requirements102% of capacity (2,551 of 2,500 PE)
Fails: BOD₅, COD
Stated cause: poor treatment performance, obsolescence
Near the fishing districts: Hron č.12, VN Závadka nad Hronom
- COV Komjaticecapacity 2,000 PE · mechanical, biologicaldoes not meet the requirements80% of capacity (1,591 of 2,000 PE)
Fails: BOD₅, COD
Stated cause: poor treatment performance, obsolescence
Near the fishing districts: Nitra č. 2
- COV Elektrosvit Vrakuncapacity 1,000 PE · mechanical, biologicaldoes not meet the requirements63% of capacity (629 of 1,000 PE)
Fails: BOD₅, COD
Stated cause: poor treatment performance, unsuitable design or capacity, obsolescence
Near the fishing districts: Žitnoostrovské kanály č. 3
- COV Canacapacity 7,500 PE · mechanical, biological, nitrogen removaldoes not meet the requirements41% of capacity (3,079 of 7,500 PE)
Fails: phosphorus
Stated cause: unsuitable design or capacity, obsolescence
Near the fishing districts: Hornád č. 1b, Olšava č. 1
- COV Chynoranycapacity 2,500 PE · mechanical, biological, nitrogen removaldoes not meet the requirements43% of capacity (1,075 of 2,500 PE)
Fails: COD
Stated cause: poor treatment performance, obsolescence
Near the fishing districts: Bebrava č. 1, Nitra č. 5b
Biggest polluters among treatment plants
The amount a treatment plant discharges into water per year
BOD₅organic pollution (oxygen demand), tonnes per year
- COV Ruzomberokcapacity 623,774 PEnear the fishing district: Váh č.18a, Čutkovo189 t
- COV Vrakunacapacity 617,817 PEnear the district: Malý Dunaj č. 6115 t
- COV Liptovsky Mikulascapacity 126,400 PEnear the fishing district: Váh č.20, Jalovecký potok and others (3)76 t
- COV Koksov – Baksacapacity 175,104 PEnear the district: Hornád č. 1b72 t
- COV Zilinacapacity 220,000 PEnear the fishing district: Váh č.12, Hričovský kanál č.2b and others (2)60 t
- COV Zeleneccapacity 211,700 PEnear the fishing district: Dudváh č. 2a, Parná č. 145 t
- COV Banska Bystricacapacity 190,830 PEnear the district: Hron č. 845 t
- COV Poprad-Matejovcecapacity 143,206 PEnear the fishing district: Poprad č. 7, Červený potok č. 1 and others (4)40 t
CODchemical oxygen demand, tonnes per year
- COV Ruzomberokcapacity 623,774 PEnear the fishing district: Váh č.18a, Čutkovo3 307 t
- COV Vrakunacapacity 617,817 PEnear the district: Malý Dunaj č. 6686 t
- COV Zilinacapacity 220,000 PEnear the fishing district: Váh č.12, Hričovský kanál č.2b and others (2)393 t
- COV Zeleneccapacity 211,700 PEnear the fishing district: Dudváh č. 2a, Parná č. 1374 t
- COV Liptovsky Mikulascapacity 126,400 PEnear the fishing district: Váh č.20, Jalovecký potok and others (3)345 t
- COV Koksov – Baksacapacity 175,104 PEnear the district: Hornád č. 1b247 t
- COV Kendicecapacity 113,788 PEnear the district: Torysa č. 2189 t
- COV Banska Bystricacapacity 190,830 PEnear the district: Hron č. 8176 t
Nitrogennutrients that feed algae, tonnes per year
- COV Vrakunacapacity 617,817 PEnear the district: Malý Dunaj č. 6214 t
- COV Koksov – Baksacapacity 175,104 PEnear the district: Hornád č. 1b154 t
- COV Zilinacapacity 220,000 PEnear the fishing district: Váh č.12, Hričovský kanál č.2b and others (2)128 t
- COV Liptovsky Mikulascapacity 126,400 PEnear the fishing district: Váh č.20, Jalovecký potok and others (3)98 t
- COV Banska Bystricacapacity 190,830 PEnear the district: Hron č. 886 t
- COV Ruzomberokcapacity 623,774 PEnear the fishing district: Váh č.18a, Čutkovo79 t
- COV Poprad-Matejovcecapacity 143,206 PEnear the fishing district: Poprad č. 7, Červený potok č. 1 and others (4)74 t
- COV Zeleneccapacity 211,700 PEnear the fishing district: Dudváh č. 2a, Parná č. 166 t
Phosphorusthe most common cause of algal bloom, tonnes per year
- COV Vrakunacapacity 617,817 PEnear the district: Malý Dunaj č. 619.0 t
- COV Ruzomberokcapacity 623,774 PEnear the fishing district: Váh č.18a, Čutkovo17.6 t
- COV Koksov – Baksacapacity 175,104 PEnear the district: Hornád č. 1b11.0 t
- COV Poprad-Matejovcecapacity 143,206 PEnear the fishing district: Poprad č. 7, Červený potok č. 1 and others (4)10.9 t
- COV Zilinacapacity 220,000 PEnear the fishing district: Váh č.12, Hričovský kanál č.2b and others (2)9.8 t
- COV Banska Bystricacapacity 190,830 PEnear the district: Hron č. 86.0 t
- COV Nitracapacity 162,000 PEnear the district: Nitra č. 36.0 t
- COV Petrzalkacapacity 171,050 PEat the fishing district: Dunaj č. 3 – Rusovecko – Jarovecká sústava ramien, Dunaj č. 4 and 2 more5.8 t
The discharged amount depends on the size of the treatment plant. Large city treatment plants therefore lead even when they treat well; what decides is the ratio to the size of the watercourse, which we do not assess here.
Where the data come from and what they do not say
- Surface waters: yearbooks of the Slovak Hydrometeorological Institute (SHMÚ) Surface Water Quality for the years 2022 to 2025. We transcribed the list of sites and indicators that failed the standard under Government Regulation no. 269/2010 Coll. into a table in the plugin. Older yearbooks are in a different format and we did not include them.
- Groundwater: SHMÚ yearbooks Groundwater Quality, stations and indicators exceeded in 2017 to 2025 according to the drinking-water limits. The connection to the fishing district is only indirect.
- Groundwater, measured values: the public SHMÚ interface "Groundwater quality monitoring results". We have actually measured values (nitrates, ammonium, iron, chlorides, metals, pesticides, PFAS, solvents) for 758 stations; for each substance we take the highest value from the samples in 2025 (for stations without data for that year, from one of the two previous years). A value equal to the standard counts as an exceedance, as it does at SHMÚ.
- Treatment plants: register of wastewater treatment plants (VÚVH, EEA) from the "Points near fishing districts" file, that is, only plants within 2 km of the fishing district line. There are considerably more treatment plants in Slovakia.
What this data does not say. The yearbook lists the sites that failed the standard. A site missing from it is not proof of clean water, so the score of a fishing district is only ever lowered and never raised. We did not include industrial polluters (the National Pollution Register) in the list because the register was unavailable when the data was collected, and for wastewater treatment plants we list only those we found near the fishing districts. Only 31% of SHMÚ sites have an exact location, 47% have only an approximate location (based on the water body, so they count less near the districts) and 22% have no location at all, so we do not assign them to any district. We determine the distance, the match of the watercourse name and the ranking ourselves; the assignment is indicative.