The high concentration of Chattonella was first observed in late April 1998 outside Hirtshals at the Danish side of the Skagerrak and spread to the western coast of Sweden and the Norwegian Skagerrak coast. This was the first time Chattonella was registered in Europe, and also the first time it had appeared in high concentrations which resulted in the death of fish. Early in May 1998 the flagellate Chattonella caused death in fish farms in an area close the southern tip of Norway. After that incident Chattonella disappeared, and was not observed blooming along the Norwegian coast due to changes in the Skagerrak circulation. However at this point in time Chattonella was observed at very high concentrations along the north and west coast of Denmark from the Jammerbugt to Esbjerg resulting in death garfish, herring and sandeel. It was feared that a new wave of Chattonella may follow the prevailing cyclonic circulation in Skagerrak and reappear at the Norwegian coast. Due to the potential danger to fish farming the situation was closely monitored and in addition to in situ measurements from ships and satellite data, an operational ecological model (NORWECOM) was used in this effort. Great amount of human made nitrate from the south part of the North Sea has probably stimulated the algae bloom.