Jordanoska, Biljana, et al. “Temporal Variability of Physico-Chemical Properties of St. Naum Karst Springs Feeding Lake Ohrid”. Macedonian Journal of Ecology and Environment, vol. 13, no. 1-2, Dec. 2010, pp. 3-11, http://mjee.org.mk/index.php/mjee/article/view/92.