Jump to content

Finnish Environment Institute | Suomen ympäristökeskus | Finlands miljöcentral

sykefi header valkoinen

Summary of the summer 2008: Unsettled summer weather prevented major algae blooms

Press release 2008-09-05 at 12:00
Finnish Institute of Marine Research and Finnish Environment Institute and the regional environment centres inform:

The algae monitoring, carried out jointly by the Finnish Environment Institute, the Finnish Institute of Marine Research, the regional environment centres and the Finnish Border Guard, is soon over for the season. The summer monitoring of algae has now continued for 11 years. As before, the weather conditions controlled the occurrence of blue-green algae. The cool and windy weather held back the growth of algae and the formation of mats during the entire season. Compared with long-term averages, the algae situation was clearly better than usual in lakes throughout the summer. In the open sea and along the coast the situation was better than usual in June and August but average in July. 

The monitoring of blue-green algae is carried out by various groups of observers: environmental and healthcare authorities, border guard pilots and voluntary citizens. The observations are made weekly at approximately 270 lake sites and 65 sea sites. More information on the sea is received from the pilots and patrol ships of the Border Guard, from automatic measurements made aboard commercial vessels and from satellite images.

Sea areas

In most years the first algae blooms in the southern sea areas of Finland are observed already in late June, but this year the rainy and chilly weather hampered the growth of blue-green algae throughout June. Particularly in the Gulf of Finland the winds caused upwelling of deep water to the surface, and the water temperature remained low in June. In the Bothnian Sea, too, the water temperature remained below 15 centigrades. No blue-green algae were observed at the surface, except along the coast of Åland where minor lumps of algae were seen.

In the beginning of July, the water temperature went up by a few grades and the amounts of blue-green algae increased in the Gulf of Finland. However, the algae were still mostly mixed with the water masses. No blooms were observed in the Archipelago Sea but around the Åland Islands there were some algae mats on the surface. In Mid-July the wa-ters along the coast of the Gulf of Finland began to cool down again, but towards the end of the month they warmed quickly up again, up  to 17 centigrades. Minor blooms at the surface were observed south of the Archipelago Sea, in the eastern Gulf of Finland and in the southern parts of the Bothnian Sea. Towards the end of the month the blooms grew somewhat larger and minor blooms were also seen along the coast of the Gulf of Finland.

August is usually the peak season for bluegreen algae blooms, but this year the blooms in August were even less than in July. There were still some surface mats in the southern Bothnian Sea, but in the Gulf of Finland the recently formed blooms were scattered by strong winds. Later in August the blue-green algae decreased everywhere in the sea areas.

The blue-green algae season 2008 can be characterized as very calm. In both June and August the quantity of blooms was well below the average, and even in July the amounts of blooms were not higher than usual.

According to the blue-green algae prognosis published by Finnish Institute of Marine Research and the Finnish Environment Institute, the risk of blooming in the Finnish sea areas was lower than last summer, and the largest blooms were expected to occur in the western and central parts of the Gulf of Finland and in the Archipelago Sea. In these areas the unsettled weather hampered the growth of blooms. In the Bothnian Sea the surface blooms occurred longer than expected.

Lakes and rivers

The windy, rainy and cool weathers hampered the growth of blue-green algae and the formation of mats throughout the summer. Blue-green algae were seen at about 10 percent of the monitored lakes which is considerably less than usual. The peak period for the blooms was early August when there were some algae at one fifth of the observed sites. The amounts of algae were in most cases small. Abundant or very abundant occurrences were seen only in 24 lakes.

The blue-green algae species found in the lakes were the same as before. Most of them belonged to the genera Anabaena, Microcystis and Aphanizomenon, and some species can produce toxins. The temperatures of surface water were throughout the summer lower than the long-term averages. Only in the beginning of July the temperatures were close to the average of that season.

The sites of the nationwide algae monitoring are located in different parts of Finland. They have been selected so that they present lakes of different size, water quality, and eutrophication status. Many lakes are not included in the monitoring, and the observations made in one part of a lake do not necessarily give information about the situation in other parts of the lake. The quantities of algae may vary between lakes and between parts of the same lake depending on local conditions and wind directions. The purpose of the monitoring is to give an overall view on the algae situation in various kinds of lakes.

Citizen’s’ Algae Phone

Due to the undramatic algae conditions the calls to the Citizens’ Algae Phone were less than usual, only around 150. During the vacation season many people asked about the algae problems of the lakes near their summer houses. A major concern was the usability of water in which there were small amounts of algae.


Target group: