A the distribution of invasive and native amphipod species in studied lakes since 2001, based on published and new data (locality codes according to Suppl. material 1). Table at each lake showing the assemblage (colours in rectangles according to different species, see legend) variation in time (symbols for sampling years: 1 – 2001; 2 – 2002; 3 – 2007; 4 – 2008; 5 – 2009; 6 – 2014; 7 – 2016). Only years of samplings from each lake and river are shown. Colourless rectangles indicate that no amphipods were recorded during the sampling. The dashed black line indicates country borders; the dashed red line indicates the Masurian tourist boat route. Black lines delimit mesoregions according to Kondracki (2002) B the assemblage composition of the amphipod fauna in studied lakes in the years 2014 and 2016 (locality codes according to Suppl. material 1). Pie charts show the relative abundances of each species. An empty circle means no amphipods were recorded. Black lines delimit mesoregions according to Kondracki (2002). Coloured dotted lines around the pie charts correspond to the lake groups: orange – I, green – II, blue – III.