Toxic algae and fish mortality in a brackish-water lake in Åland, SW Finland

Tore Lindholm*, Petra Öhman, Katriina Kurki-Helasmo, Brendan Kincaid, Jussi Meriluoto

*Corresponding author for this work

Research output: Contribution to journalArticleScientificpeer-review

79 Citations (Scopus)


The brackish-water Lake Vargsundet (SW Finland) was affected by multiple algal toxins and extensive fish mortality in July 1997. Dense populations of the ichthyotoxic haptophyte Prymnesium sp. and the hepatotoxic cyanobacterium Planktothrix agardhii were observed simultaneously, but usually in distinct layers. Fish died in the relatively clear epilimnion where 10-40 million Prymnesium cells per litre were recorded (chlorophyll a range 6-18 μg l-1). Fish survived in the metalimnion dominated by the hepatotoxic P. agardhii (chlorophyll a 20-40 μg l-1). The deeper layers were anoxic. The Prymnesium-rich water remained ichthyotoxic until the end of August but the toxicity was less marked in tests with Artemia salina. As even inconspicuous haptophyte blooms with low chlorophyll a concentrations may be harmful, safety and monitoring issues need reconsideration.

Original languageEnglish
Pages (from-to)109-120
Number of pages12
Publication statusPublished - 1999
MoE publication typeA1 Journal article-refereed


  • Fish kill
  • Microcystin
  • Planktothrix
  • Prymnesin
  • Prymnesium
  • Toxic algae


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