Odra

Key information

• The first seasonal bloom of the “golden alga” occurred in June 2025 in the Gliwice Canal.
• Due to persistently high concentrations of the algae in the following weeks and a significant risk of its migration into the Oder River, in July the Interministerial Team for the Oder River decided to dose hydrogen peroxide in the Kłodnica River (which connects the Gliwice Canal with the Oder). The intervention lasted several days and produced the expected results: no “golden alga” was detected in the Oder River
• The second bloom occurred in September 2025; however, due to reduced water flow in the Gliwice Canal, it was contained in the upper sections of the canal.
• Since early October 2025, the “golden alga” has disappeared from the Gliwice Canal and is no longer detected in the Kłodnica River or Lake Dzierżno Duże. However, its presence is still recorded in Farskie Lake (at an alert level).
• Thanks to prepared and implemented crisis management procedures, as well as continuous water monitoring and implementation of recommendations, no presence of the “golden alga” was detected in the Oder River in 2025, despite highly unfavourable hydrological conditions in the basin.

Systemic measures for protection against “golden alga” blooms

The Interministerial Team for the Oder River, alongside ongoing crisis-response activities, is also working on systemic solutions aimed at eliminating the root cause of “golden alga” development in the basin, which is high salinity.

Reducing excessive salinity in the Oder requires appropriate legal regulations, organisational changes, and investments in retention systems and desalination facilities. This requires cooperation across several ministries; therefore, the Interministerial Team for the Oder River, operating under the Ministry of Climate and Environment, includes representatives of the Ministry of State Assets, the Ministry of Infrastructure, the Ministry of Energy, and the Ministry of the Interior and Administration.

As part of measures addressing the root causes of “golden alga” blooms, the Ministry of Climate and Environment developed the “Investment Plan for the Mining Sector Aimed at Reducing Salinity in the Oder River Waters – Phase I to 2030”. The document includes three main components:

• restructuring component – gradual phase-out of mines in line with the schedule defined in the so-called “Social Agreement”;
• Technological / research and development component – implementation of innovative technologies and construction of a pilot installation for salinity reduction.
• investment component – development of retention and dosing systems enabling effective management of saline water discharges.

Figure 1: Projected reduction in Oder River salinity by 2030

Actions included in Phase I of the Plan are expected to reduce salinity levels by 60% in Lower Silesia and by 15% in Upper Silesia during the summer period. Phase II of the Plan will be developed following the results of the pilot innovative technology and additional analyses. After interministerial consultations, the Plan was adopted by the Economic Committee of the Council of Ministers on 24 October 2025.

Oder monitoring and the situation on the Vistula

The risk of recurrence of an ecological disaster in the Oder appears every year; therefore, the condition of the Oder basin is monitored by the Chief Inspectorate for Environmental Protection (GIOŚ) under intervention monitoring. Data are analysed by the Interministerial Team for the Oder River, which issues recommendations for relevant authorities.

Intervention monitoring of the Oder includes measurements of physicochemical parameters (including temperature, salinity, oxygenation, and pH) and analysis of the abundance of “golden alga” cells per litre of water. Samples are collected regularly: during the spring–summer season once a week or more frequently if analyses indicate the presence of the algae. Based on monitoring data, ad hoc measures are implemented under the “Prymnesium parvum (‘golden alga’) intervention monitoring procedure”. This monitoring is specifically designed to assess the risk associated with the development of this organism, track its dynamics in the Oder and affected water bodies, and confirm its presence in potential outbreak areas.

The main outcome of intervention monitoring is risk classification (alert level and Levels I, II, and III of threat). Results are available at badania.gios.gov.pl/odra/ as an interactive map presenting both current and historical data.

In addition, the Interministerial Team for the Oder River is working on expanding the automatic monitoring network for rivers. In 2025, GIOŚ, as the institution responsible for environmental monitoring in Poland, in cooperation with the National Fund for Environmental Protection and Water Management (NFOŚiGW), launched a pilot automatic monitoring system on the Oder. The pilot includes ten measurement stations. This is an interim solution pending amendments to the Act on Environmental Inspection, which are intended to systematise automatic monitoring. The first stations have already been installed. Sensor and data transmission system tests are currently underway to enable the start of monitoring in April 2026, before the period of increased risk of “golden alga” blooms.

As part of GIOŚ monitoring, in addition to intervention studies in the Oder basin, samples from the Vistula River are also analysed. In 2025, no presence of the “golden alga” was detected in the Vistula.

Monitoring results, scientific data, and information on mitigation measures to improve the ecological status of the Oder are regularly shared with the German side within the framework of an international expert group.

Unfavourable hydrological conditions in 2025

According to the Institute of Meteorology and Water Management – National Research Institute (IMGW-PIB), although January 2025 was not dry, February, March, and April were classified as very or extremely dry. Rainfall in May did not improve the hydrological situation. In summer 2025, low water levels dominated rivers, and hydrological drought intensified. By early September, 65% of hydrological stations were in the low-water zone. In September 2025, the Vistula River reached its lowest level in recorded history; on 2 September at the Warsaw-Bulwary gauge, the water level was only 4 cm with a flow of approximately 154 m³/s. Hydrological drought also affected the Oder and its tributaries, creating additional unfavourable conditions conducive to algal blooms and fish mortality.

During the 2025 summer season, 4.5 tonnes of dead fish were removed from the Oder and the Gliwice Canal, of which approximately 250 kg were associated with the “golden alga”. The remaining fish kills were attributed to viral infections or low oxygen levels. No presence of the “golden alga” was detected in the main channel of the Oder.

Figure 2: River water level zones in Poland, status as of 5 September 2025

Source: IMGW-PIB

Figure 3: Hydrological drought warnings in Poland, status as of 5 September 2025

Source: IMGW-PIB

Plans for 2026: implementation of the “Clean Oder” programme

In the next season, the Interministerial Team for the Oder River will continue activities related to ongoing monitoring of the “golden alga” risk. It will also coordinate long-term measures under the “Clean Oder” programme, including:

• expansion of the automatic surface water monitoring network in Poland;
• launch of a dedicated financing instrument accelerating local renaturation projects restoring fish migration in tributaries and strengthening ecosystem resilience;
• pilot testing of innovative technologies to reduce desalination costs as part of Phase I of the mining sector investment plan;
• strengthening nature protection, including the unique Lower Oder Valley.

Current information on the work of the Interministerial Team for the Oder River, monitoring data with an interactive map, and analyses of “golden alga” risks are available on the official Oder website.