- 4 - 
Due to a change in water level in the Baltic Sea an outflow from the Szczecin Lagoon into the 
Baltic started on 20 July 1997. The flood water from the Odra river started to fill the Zalew 
Wielki on 23 July 1997. The maximum inflow occurred on 7 August 1997. The water of 
Zalew Wielki was replaced by the river water after about 5 days. The Kleines Haff was only 
slowly filled with the flood water. It reached the western end of Kleines Haff around 13 
August 1997. 
In the most affected central and eastern area of the Lagoon an increase of all inorganic 
nutrients was observed in the course of the flood. With respect to nutrients only a small 
fraction was transformed to biomass. 
Concentrations of heavy metals zinc, copper and nickel did not show any significant changes 
in water compared to previous studies, but slightly increased concentrations of lead, cadmium 
and mercury were observed. 
A large number of pesticides (26) were analysed from sea water in the Szczecin Lagoon. Two 
pesticides (atrazin and 2,4-dichlorphenoxy acetic acid) were observed in measurable 
concentrations. 
Reduction of soft bottom macrofauna was observed at the entrance of the river into the 
Lagoon. The dominant species in the central and north-eastern parts of the Lagoon did not 
exhibit significant effects of the flood. 
3. Developments in the open sea 
Gulf of Gdansk 
Flood water from the river Vistula reached the Gulf of Gdansk on the turn of July and 
August 1997. In general southward flow from the open sea pushed flood water towards the 
coast of the Gulf of Gdansk in westerly and easterly directions. In the Gulf of Gdansk nutrient 
concentrations were of the order of maximal concentrations recorded in spring thaw waters 
during 1979-1996. 
Considerably increased primary production followed the inflow of nutrient-rich flood water 
into the Gulf of Gdansk, which was also observed as an increase in oxygen saturation. At the 
same time large amounts of settling organic matter led to temporary oxygen deficiency in 
near-bottom water. 
Increased nutrient concentrations were limited to the geographical boundary of the Gulf and 
did not spread into the open Baltic. In the Gulf of Gdansk most of the measured parameters 
returned to normal conditions in November 1997. 
In the Gulf of Gdansk the impact of flood waters on the sanitary conditions was significant. 
With respect to parameters such as total bacteria number, MPN (Most Probable Number) of 
faecal coliform bacteria and MPN of faecal streptococci, the sanitary pollution of the Gulf of 
Gdansk was several times higher than in previous years. Potentially pathogenic bacteria were 
isolated from near-shore water of the Gulf of Gdansk. In autumn the situation returned to 
normal. 
Pomeranian Bav 
Main discharge into the Pomeranian Bay started with an increase in the discharge and existed 
until the end of August with short interru prions. The early increase occurred after a blocking