Summary reviews

The cyanobacterial situation in the past summer has varied according to changing weather conditions. Cyanobacterial levels in sea areas and lakes peaked during the hottest periods of the summer in mid-July and mid-August. The cooler weather in late July and early August curbed the growth of cyanobacterial blooms for a while. In lakes, this summer’s cyanobacterial situation remained quite typical compared to previous years.

During the summer, the cyanobacterial situation has varied in both Finnish lakes and sea areas. The amount of cyanobacteria was exceptionally at its peak in the sea areas already in mid-July. Even in inland waters, the sunny and calm weather of early summer, as well as the warm waters, accelerated the growth of cyanobacteria, and as a result cyanobacteria began to bloom earlier than usual at many of the national algal monitoring sites.

The cyanobacterial situation over the past summer has been variable both in inland waters and sea areas. The number of cyanobacterial observations during June–August followed the weather conditions quite closely. In lakes, coastal areas and the archipelago, the cyanobacterial summer began earlier than usual as a result of the warm early summer. In July, the cyanobacterial situation was calmer due to the cooler weather, but in mid-August, warm weather again enriched the cyanobacterial blooms.

During the past summer, large amounts of blue-green algae (cyanobacteria) were seen particularly in the northern part of the Baltic Sea’s main basin, at the entrance to the Gulf of Finland and south of the Åland Islands. Blue-green algae were observed as surface rafts at time to time, but the wind mainly kept it mixed in the water. In lakes, blue-green algae were seen mixed in the water and less large surface blooms were observed than in earlier monitoring years.

The algal situation in early summer was calm and cyanobacteria started to become more abundant only in July. In sea areas, cyanobacteria occurred abundantly especially in the northern Baltic proper and the western Gulf of Finland, but winds and cool seawater prevented the formation of conspicuous surface accumulations. In lakes, on average fewer observations of cyanobacteria than usual were made, with the exception of early July and late August.

Cyanobacteria started to increase in abundance early this summer, but during late summer less cyanobacteria surface blooms were observed than normally. In the Finnish southwestern open sea areas cyanobacteria were abundant throughout the summer, but mixed in the water column, and long-lasting surface blooms did not develop. In lakes, cyanobacteria were abundant only occasionally during the summer, but in August exceptionally little cyanobacteria was observed.