Phytoplankton community structure in the Gopło lake, phytoplankton hitch-hikers infiltrated into beakers through plankton nets and their fate after ten days of incubation in filtered lake water from the Kierskie lake without and with resident T. obliquus (Resident(–), Resident(+); respectively). Abbreviations: CYANO – Cyanobacteria, CRYPT – Cryptophyceae, BACILL – Bacillariophyceae, CHLOR – Chlorophyta, DINOP – Dinophyceae, HAPTO – Haptophyceae, EUGLE – Euglenophyceae, CHRYS – Chrysophyceae.