BENTHOS OF LAKE ORTA IN THE YEAR 1996.

Lake Orta has been interested since 1926 by severe industrial pollution, due to the effluents of a rayon (artificial silk) factory that discharged huge amounts of copper and ammonia. As a consequence, the benthic fauna faced noticeable changes, becoming extremely poor in species. However, after extensive liming (in 1989-90), the biotic communities of the lake showed many signs of recovery , and in 1996 it was decided to study the benthos composition and abundance in detail, to assess whether the lake restoration resulted in a complete recovery of this biotic compartment. Actually, both the small number of taxa, and the low abundance of the benthos, indicate that the sedimentary environment is still very stressed. In fact, albeit this study shows that benthos fauna is actively recolonising Lake Orta bottom, spreading from river mouths, in 1996 the benthic community cannot be considered fully organised.