Few studies exist documenting changes in rotifer communities over long time intervals. Here, we explore seasonal and long-term variation in rotifer communities in four Polish lakes sampled in 1976 and again in 1997. Rarefied, asymptotic species richness did not differ significantly across study years, although values in 1997 tended to be higher. Simpson's and Shannon-Wiener diversity measures provided inconsistent temporal results, with only the former indicating significantly higher richness in 1997. Sorensen's coefficient of community similarity was as high among lakes in 1976 (0.81) and in 1997 (0.76) as within lakes across the 21-year span (0.77). Nonlinear redundancy analysis of species' abundances revealed large, consistent seasonal changes across lakes, smaller consistent shifts between sampling periods, and small differences between lakes. Collectively, these metrics indicate that species composition was relatively stable among lakes within years and within lakes between years, while species' abundance patterns were far more variable and most affected by season.

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