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Water quality improving – will algal blooms decrease?

Algal situation in inland waters in 1998–2015

Algal situation in inland waters

Algal situation in sea areas in 1998–2014

Algal situation in sea areas
The illustration shows the range for each year's algal barometer, i.e. the highest and lowest rating and median for weeks 23–35, from early June to the end of August. The algal barometer is an index based on observations of national algal monitoring. It enables a weekly assessment of the overall algal situation in inland waters and sea areas.
In summer 2015 there were too few monitoring spots and therefor barometer was not updated.
Source: National algal monitoring, Järviwiki, SYKE and ELY Centres and environmental authorities in municipalities. 2015.


It might be assumed that eutrophication in waters is slowing, since nutrient discharges from point sources have considerably decreased in recent decades. However, recovery can be slow if a high quantity of nutrients has accumulated in the sediment. These nutrients can return to the water in a process called internal loading thus maintaining levels of eutrophication.

Blue-green algal blooms in summer are among the most prominent problems caused by eutrophication. Their occurrence has been systematically monitored since 1998. The impetus for monitoring came from the record-breaking summer of 1997, with its disastrous algal situation and exceptional level of algal blooms in both the Baltic Sea and lakes. Large amounts of toxic algae drifted ashore and some people exhibited symptoms of poisoning.

Algal bloom monitoring comprises visits to around 300 permanent observation sites once a week from June to September, in order to record the occurrence and amounts of blue-green algae. To facilitate assessment of the situation as a whole, an algal barometer index is calculated based on each week's observations. The level of the index depends on the number of observations of algae and the quantities observed.

Different years can be compared by examining the most typical values given by weekly algal barometer indices. In 2008–2015, most algal barometer readings were lower than in earlier years of algal monitoring.

Annual variations in the algal situation are explained by changes in nutrient levels and variations in summer weather.


  • National algal monitoring. Lakewiki. Finnish Environment Institute, ELY Centers and environmental authorities in municipalities. 2015.


Published 2015-10-15 at 14:51, updated 2015-10-15 at 14:46