Potamogeton ×salicifolius Wolfg., the hybrid between P. lucens L. and P. perfoliatus L., is recorded from north-eastern Poland for the fi rst time. The new station is located in the Wigry Lake (the Wigry National Park), within FB19 square unit of the ATPOL cartogram grid. The distribution is updated with one new population of vegetative ramets.
Potamogeton lucens L., and Ceratophyllum demersum L. were collected monthly in two ecosystems in Al-Hammar marsh with clear and turbid water. The dominant species of epiphytic algae at both stations and plants were Achnanthes minutissima Kütz., Cocconeis placentula var. euglypta (Ehr.) Cl., and Fragilaria spp. The cell number showed seasonal variation both on plants and at stations, but in general there were no distinct differences in algal species and population density between the two macrophytes in each area. Marsh with turbid water offered better conditions for algal growth thanks to nutrient enrichment.