Eutrophication status 2007-2011

The entire open Baltic Sea was assessed as being eutrophied (Figure 1). Coastal areas in Orther Bucht (Germany), outer coastal Quark (Finland) and outer coastal Bothnian Bay, outer coastal Bothnian Sea and inner and outer coastal Quark (Sweden) were the only coastal areas assessed b​y national authorities as being in good ecological status.​

Eutrophication_Status07_11_withI_inset.jpgFigure 1. Eutrophication status in 2007-2011 was assessed as being affected by eutrophication in the entire open Baltic Sea (red colour, status less than good; sub-GES). Outer coastal waters of the Quark (Finland) and in Orther Bucht (Germany) were assessed by national experts to be in good ecological status. For methodology, see Technical data information in the complete report.


This result indicates that despite measures taken to reduce external inputs of nitrogen and phosphorus to the sea, good status for eutrophication has not been reached yet. Nearly the entire sea area is still affected by eutrophication.​

​The open-sea areas most affected by eutrophication are the Gulf of Finland, Aland Sea, Gulf of Riga, Western Gotland Basin, Eastern Gotland Basin, Bornholm Basin, Gdansk Basin and Arkona Sea (Figure 2).

EUTRO_Status_v2_withoutcoast.pngFigure 2. Eutrophication status in 2007-2011 expressed as Eutrophication Ratio, showing roughly the distance to GES (where ER = 1). For detailed information, see the complete report.

Differences​ between this core indicator-based assessment and the assessment for years 2001-2006 were found in two of the 17 open-sea areas. The Swedish waters in the northern Kattegat as well as the open Bothnian Bay, which both had good status in 2001-2006 are now affected by eutrophication (HELCOM 2009). In the Kattegat, the discrepancy between 2001 and 2006 and this assessment may be a result of methodological differences between the two assessments, or it may be that the northern Kattegat is close to GES. In the Bothnian Bay, the status decrease is mainly due to change in the status of the chlorophyll-a indicator.

Eutrophication is driven by a surplus of the nutrients nitrogen and phosphorus in the sea. Nutrient over-enrichment causes elevated levels of algal and plant growth, increased turbidity, oxygen depletion, changes in species composition and nuisance blooms of algae.

The main pathways of nutrients to the sea are riverine inputs, atmospheric deposition of nitrogen to the water surface and direct waterborne discharges to the sea either from coastal point sources, run-off from diffuse sources in coastal areas and discharges from ships. In addition, excess nutrients stored in bottom sediments can enter the water column and enhance primary production of plants.

Access the full assessment available here

Results of the HELCOM Eutrophication Assessment Tool, 2007-2011 - HEAT3 2007_2011 final.xlsm

Editors: Pyhälä M, Fleming-Lehtinen V and Laamanen M

Authors: Lysiak-Pastuszak E, Carstens M, Leppänen J-M, Leujak W, Nausch G, Murray C and Andersen J