The results of the water samples taken in response to the report of dead fish in Lake Varna are now available.

Minor exceedances were found for BOD5 and total nitrogen, and exceedances of the standards for ammonium nitrogen and total phosphorus ranging from 6.3 to 7.6 times the limit were observed. The results for pH (8.36) and dissolved oxygen meet the standards for good water status. The water temperature at the time of sampling was 22.2 °C. At a pH above 7 and high water temperatures, some of the ammonium ions are converted into ammonia, which is toxic to fish and causes their death.

A report of dead fish in Lake Varna, near the “Lesport” port, was received at 4:00 p.m. on June 13. An immediate inspection was conducted by the Black Sea Basin Directorate (BSBD) – Varna, the Regional Inspectorate of Environment and Water – Varna, and the Regional Laboratory – Varna of the Executive Environment Agency in the area between the villages of Ezerovo and Kazashko.

Phosphates are not toxic to fish, but high concentrations of them stimulate the growth of algae naturally present in the water, which can lead to a decrease in dissolved oxygen levels and fish mortality.

According to the expert assessment, the elevated concentrations of ammonium nitrogen and total phosphorus may be linked to a recent unauthorized discharge of domestic sewage, wastewater from industrial facilities in the Devnya Lowlands, and/or activities related to shipping and port infrastructure.

The BDCHR notified the Regional Inspectorate of Environment and Water – Varna and the Executive Agency “Maritime Administration” under the Ministry of Transport and Communications of the results of the sample analysis so that they may take follow-up actions within their respective jurisdictions.