Kartuzy Lakes, Poland

For Demo sites: Successful restoration of four lakes complex, affected by domestic and industrial sewage in the past.

For Innovation Measures: P-recovery from lake sediments.

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Site description

Kartuzy Lakes complex consists of four lakes - Mielenko Lake (area 0.079 km², max depth 1.9 m), Karczemne Lake (area 0.40 km², max depth 3.2 m), Klasztorne Małe Lake (area 0.139 km², max depth 20 m) and Klasztorne Duże Lake (area 0.512 km², max depth 8.0 m) - located in Kartuzy City. The lakes are connected by Klasztorna Struga Stream, forming a lake-river system. In the 20^th century Kartuzy Lakes were subjected to massive pollution from the inflow of raw domestic and industrial wastewater, which led to a deterioration of their water quality. Particularly, lakes Karczemne and Klasztorne Małe were the most polluted, with dense blooms of phytoplankton and cyanobacteria, low water transparency, and with active internal loading of nitrogen (N) and phosphorus (P) from the polluted sediments. The main challenge for the restoration of good ecological status and water quality improvement is the high nutrient legacy present in the lake sediments. The main aim of the restoration measures taken is to restore the possible use of Kartuzy Lakes by the local community.

Restoration measures applied

On two lakes (Klasztorne Małe and Karczemne) artificial mixing was implemented in the 1980’s, but this had little effect. The first attempt of P inactivation (using LMB in 2006) on Klasztorne Małe Lake also failed. The main reason of failure was the lack of raw sewage diversion. Protective measures in the lakes’ catchment (modernisation of sewerage system and sewage diversion) were made in 2016-2018. Then it was possible to design proper restoration methods.  Because of the active internal loading in Kartuzy Lakes, the P inactivation (using iron and aluminium coagulants) was implemented on all lakes (2020-2023). In shallow Karczemne Lake, where sediment P legacy was extremely high, sediment dredging was applied (removed sediment volume 240,000 m³) and P-inactivation was implemented after polluted sediment removal. Dredged sediment was directed to the local WWTP via a pipeline, where a special technological line was constructed for sediment treatment and transformation into fertilizer for agricultural use (Circular solution). In total, more than 1 million m³ of sediment-water mixture was treated. Biomanipulation of fish structure in lakes was also carried out as a supportive method throughout the whole project. All restoration activities were completed in 2023.

Current goals of restoration at the site

Current goal is observation of Kartuzy Lakes ecosystem reaction to applied restoration measures. Development of lakes use by local community, and social benefits analysis, as well as assessing sediment P application for agriculture as an example of developing a sustainable circular economy.  

Sectors involved in lake basin management

Fisheries and angling sector, leisure and recreation.

Further reading