Ten years of data on the presence of surfactants (compounds used in cleaning products such as laundry soap) in the Warta at Poznań found declines in anionic surfactants but a substantial (six-fold) increase in nonanionic surfactants during the 1990s. Some of this change reflected the changing ratio of these compounds in cleaning products themselves, but that alone would not account for the size of the increase in nonanionic surfactants. Data from measuring stations at other points along the river indicated that concentrations of nonanionic surfactants were highest downstream of the industrial cities of Czestochowa, Sieradz, and Gorzow. High concentrations were also found on the Ner river downstream of Łódź, where the anionic surfactant concentrations “were more similar to those of a raw sewage than surface water.” (Szymanski et al. 2001: 375) Fish populations, species diversity, and size and weight provide indirect indicators of water quality improvement or decline. For the most part, data on fish in the Warta River indicate that water quality still needs considerable improvement. In the farthest upper reaches of the Warta river, where water quality is significantly impaired by mining and other industrial discharges, no fish are found. (Przybylski 1996: 40) The next river portion—the stretch of the upper Warta between the Poraj and the Jeziorsko reservoirs, along which the riverbed and banks are natural—exhibits eutrophication problems but the highest fish population, growth rates, sizes, and species diversity. (Przybylski 1996; Penczak et al. 1998) Both species richness and species diversity in the Warta drop dramatically along the stretch of the Warta from the Ner mouth to the Prosna mouth. (Przybylski 1993: 508) “Drastic changes in the fish fauna composition were noted in the polluted parts of the upper Warta, especially in the part above the inflow of the Ner River (pollution from the city of Łódź, via the Ner). In this part of the river, the species number is reduced to a minimum value of four.” (Przybylski 1993: 506) Along the middle of the Warta’s course, a large and statistically significant drop in species richness and diversity occurs between the river stretches above and below the Jeziorsko reservoir. The number of species and their population and size were recorded at selected sites above and below the dam over an 11-year study period, 1985 (the year before the dam was built) through 1995 (Penczak et al. 1998; Penczak 1999; Glowacki and Penczak 2000). In the 10 years after the river was impounded, the number of fish species found below the dam decreased two- to three-fold while the number in the natural river course above the dam remained relatively constant.<sup>18</sup> Even after 10 years, the size and weight of fish did not recover to pre-impoundment levels upstream or downstream of the dam (Penczak 1999).

The Jeziorsko dam has no fish ladder, which obviously accounts for some of the negative impact on fish population. Two migratory species found in the river before the dam’s construction became extinct thereafter (Penczak et al. 1998: 168). Even nonmigratory fish below the dam are fewer in number and species diversity, and smaller in size. Some effects on non-migratory fish may be due to impacts on water temperature from the hydroelectric power plant at the dam—since the dam was completed, there has

> 18 There was a sharp but temporary drop in fish population and species diversity above the dam in March 1989, when the trees and other vegetation along the riverbank were cleared.  The population rebounded over the next three years as the vegetation grew back. (Penczak 1995a)

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