Coenagrion armatum is a critically en- dangered species in Poland which has been vanishing in the western part of the country. Its refuge is eastern borderland, however, no contemporary existing populations have been found from the northern part of this area so far. The author gives the description of the first site of C. armatum known from Polish part of the Lithuanian Lake District: Lake Gulberek NE from Wiżajny (54°23 ’44” N, 22°55’26” E, 220 m. a.s.l., UTM: FF22).