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Non-indigenous invasive aquatic plants affect macrophyte community composition, structure and abundance, and are recognised as one of the major causes of biodiversity loss in aquatic ecosystem. Their mass development poses serious ecological, sociological and economical threats in many countries. We investigated biological, physicochemical, hydromorphological and geographical data from 447 Polish lowland lakes to recognise the phenomenon of invasive macrophyte species and to identify environmental factors that determine their occurrence and abundance. We focused on Elodea canadensis (EC) as the most common and widespread alien hydrophyte in Poland. Phytocoenoses of EC were present in 40 % of analysed lakes. The area occupied by EC ranged from 2.3 to 5.5 % of the total vegetated area per year, on average, with a maximum of 37.8 %. A comparison between two sub-periods (2005-2009 and 2010-2013) revealed a lack of increase in EC mean abundance within the analysed period. Likewise, no evidence of EC effects on the native flora, its richness and diversity and no effects on the ecological status of the lakes were found. In the analysed period, EC did not demonstrate invasive character in Polish lakes. The habitat preference of EC was biased towards larger and deeper lakes located at higher altitudes, with longer water retention times, better water quality and better ecological status based on macrophytes compared with non-invaded lakes. We found altitude and water quality as the main determinants of EC occurrence within the sampled area. We suggest that both climate warming and accelerated eutrophication may contribute to reducing EC spread in Europe observed during recent decades. Keywords Canadian waterweed Á Alien species Á Invasive plants Á Macrophytes Á Lakes Á Poland Electronic supplementary material The online version of this article (

The Lake Habitat Survey for Polish Lakes (LHS_PL) is a method for the hydromorphological investigation of lakes employed for the assessment of the ecological status of surface water bodies in Poland. It was developed based on the British Lake Habitat Survey method. In 2015, after almost a decade of work on the adaptation, the LHS method was finally adjusted to Polish conditions, and since 2016, it has been implemented in the State Environmental Monitoring programme. This paper presents the assumptions and evolution of the method and the approach for determining boundary values for the high/good (H/G) and good/less than good (G/LTG) ecological status classes. The method involves the assessment of the morphological features of the lake and anthropogenic pressures at 10 observation plots as well as the analysis of hydrological alterations and anthropogenic activities within the lake basin and the entire catchment area. The data collected in the field are used to calculate the index of lake hydromorphological alteration, that is, the Lake Habitat Modification Score for Polish Lakes (LHMS_PL). The LHMS_PL values range from 0 to 144, where 0 means no modification and 144 refers to a hydromorphologically highly modified state. The boundary values for the H/G and G/LTG status classes have been determined using the quartile method based on the relationship between hydromorphological modifications of lakes and the condition of the phytoplankton and macrophyte communities therein.

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Water level fluctuations (WLF) in lakes are a natural feature that can be modified by human activities. The article presents a review of literature on the water level fluctuation in Polish lakes, their amplitude, periodicity and trends. WLF controlled by natural conditions and also those induced by human activity were considered. Although anthropogenic water level fluctuations in most Polish lakes seem to fall within the range of natural fluctuations, in some cases economic activities (e.g. the use of lakes for energy generation purposes) can lead to strong disturbances of the hydrological regime, causing an ecological instability that makes it impossible to maintain/achieve good ecological status. This, in turn, makes it necessary to define good ecological potential, being an environmental objective for such water bodies, which is less rigorous compared with good ecological status. The article indicates the need to expand the methods for the assessment of lakes in the country with new biological indicators to assess, in accordance with the Water Framework Directive requirements, the impact of hydrological alterations on biota

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A multitude of spatial relations between the lake and its catchment prompts both water managers and scientists to use Geographic Information Systems (GIS). The paper presents the possibility of using GIS systems in the monitoring and management of Polish lakes, taking advantage of the dynamic development of geoinformatics. The focus is on the possibility of using GIS systems when creating documents necessary for the implementation of subsequent water management plans, as required by the Water Framework Directive. This review presents the currently existing spatial databases of Polish lakes and discusses the impact of the use of morphometric data of lakes on the process of water monitoring. Attention was paid to the problem of delimiting the catchment areas of lakes and the legal consequences of determining their boundaries. Tools used in the interpolation of limnological parameters and the models most often used in GIS software for water quality prediction are discussed.