Twelve reservoirs in North-West Bulgaria were sampled in autumn 2009 to study the species diversity and
distribution of benthic macroinvertebrates in relation to some environmental parameters, and to assess the
ecological potential of the reservoirs based on macroinvertebrate metrics. A total of 75 taxa belonging mostly
to Oligochaeta, Ephemeroptera, Chironomidae, and Mollusca were recorded. The most abundant were the
invasive bivalve mollusks Dreissena sp., larvae of Ch. crystallinus and oligochaetes. The highest taxa diversity
was recorded in the reservoirs located in close proximity to the Danube River and in the reservoirs with
the largest areas. The occurrence and abundance of invasive Dreissena species, electrical conductivity, Ca2+
concentration and water transparency were identified as potential factors for the mactroinvertabrate distribution.
Based on 7 macroinvertebrate metrics, the ecological potential of the reservoirs was assessed in the range
from “Good” to “Bad”. Most of the reservoirs were classified as having a “Moderate” ecological potential. It
is recommended that the invasive alien species are considered in the use and development of macroinvetebrate
metrics and assessment tools for lakes, and in the river basin and reservoir management strategies. Immediate
management actions are crucially needed to improve the ecological potential of reservoirs.