Italian lakes

Italy possesses around 500 water bodies with a surface greater than 0.2 km2. The volume of water contained in these basins is around 150x109 m3. Such a quantity at first sight would appear very large, were it not for the fact that the water is distributed unevenly over the national territory and is concentrated mainly in the north of Italy. Around 130 billion cubic meters of water are in fact concentrated in the great lakes south of the Alps: lakes Maggiore, Orta, Iseo, Lugano, Como, and Garda Of the remaining 20 billion cubic meters, a large proportion belongs to a second important lake district, located in Central Italy, and including Lakes Bolsena, Bracciano, Vico and Trasimeno. Only a small proportion (about 3% of the total) is therefore distributed in the southern regions of the country, in reservoirs specially created to solve or at least alleviate the serious problem of supplying water for drinking or irrigation purposes. It should however be noted that the volume of water contained in these reservoirs is highly subject to annual fluctuations closely connected to the quantity of precipitation and to the climatic conditions of the locality; in particularly dry seasons these may cause the reservoirs to dry up almost entirely. As an example, in Sicily in summer 1993, the thirty reservoirs created to collect water for drinking and irrigation contained only around 20 % of their potential volume. In this small atlas of Italian Lakes you can found, for the most important water bodies: => main morphological features => bathimetric map => data on trophic state and pollution => bathing information (only for lakes Maggiore, Orta and Mergozzo) The importance of the great lakes as water resource, because of their volume and the variety of possible uses for their water, is widely accepted; however it should be noted that even the small lakes have considerable socio-economic importance. These latter lakes, thanks to their distribution over the territory, do in fact ensure the performance of a number of social and economic activities, as well as being important for their ecological and environmental value. In many areas of the country, the very presence of these 'small' water bodies has been the factor determining the development of important human activities. Accordingly small lakes environments also require a careful management policy to ensure that they. are kept 'in good health' when their environmental conditions are still acceptable, or which will facilitate their recovery when their conditions hare deteriorated over time. The Italian lakes, like all lakes in developed countries, are affected in three main ways which lead to a deterioration in their water quality: -the process eutrophication, due to excessive loads of nutrients (phosphorus and nitrogen); -acidification processes caused by the acidity. of atmospheric depositions; -processes of pollution by toxic compounds due to the dumping of untreated or inadequately treated industrial waste into rivers, soil and ultimately into lakes. However, the primary and the most widespread, problem for Italian lakes remains without question that of eutrophication, as regards the lakes located at low altitudes. Acidification is the problem for alpine lakes. The pollution of lakes by toxic substances is in Italy fortunately a rare event affecting fewer then ten lakes and among them Lago d'Orta, the most impressive example of this kind of pollution till the beginning of this decade, when an effective restoration treatment was undertaken. Alpine lakes: The most important environmental problem concerning water quality in high altitude lakes is the acidification. Since the beginning of the 70s, researches on the quality of atmospheric precipitation have been undertaken. Further studies were performed in the frame of E.U. programs in collaboration with countries (such as Switzerland and Austria) involved in the problem. A databank has been created for 650 lakes, 510 of them Alpine. While only 1 % of subalpine lakes are classed as sensitive to acidification, the figure rises to 52 % in the case of Alpine lakes As for the levels of acidification reached by the various lakes according to observed pH values, 2 % of the lakes studied have pH values lower than 5.3 units (the figure below which the lake biocenosis suffers extensive damage), with 5 % of the lakes showing pH values lower than 6 units. Lowland lakes and reservoirs Most of the lowland lakes and reservoirs in Italy, irrespective of their size and geographical location, are subject to more or less severe eutrophication processes. Among the natural lakes, those located in the subalpine area are particularly important because of their size and volume, as well as their location, in the most highly populated and industrialized area in Italy. The subalpine lakes were originally oligotrophic. The trends of phosphorus, the element limiting the primary production, provide a valuable information on the lakes' trophic trends The increase in phosphorus concentration first involved the deepest basin of Lake Lugano, which reached in the second half of the seventies the concentration of 150 µg P l-1. Lakes Como, Maggiore and Iseo underwent an increase in phosphorus concentrations in the sixties and reached their highest values at the end of the seventies. In the following years, concentrations decreased in Lake Como and particularly in Lake Maggiore, where the present (1998) values are <10 µg P l-1. In the case of Lake Iseo, the mean concentrations remained steady on values of about 30 µg P l-1 during the period 1975-1985, after which an increase was observed to the present values of ~ 50 µg P l-1. Lake Garda showed the lowest phosphorus concentration among the southern Alpine lakes, with values lower than 10 µg P l-1 in the seventies and the early eighties; since 1986 values have shown a little increase. In the north of the country there are several others lakes which are, in spite their smaller size, of great importance as source of water for drinking, industry and irrigation. Most of them are eutrophic because of the sewage pollution and of fertilizers drained from the watershed. A third group of lakes, important because of their large size and depth, is located in Central Italy. They are mainly of volcanic origin and they are all in eutrophic conditions, although efforts are being made to improve the situation.

Most largest lakes of Italy
in order of greatness

	Lake	Km²	Region
1	Garda	370	Lombardia-Trentino Alto Adige-Veneto
2	Maggiore	212	Lombardia-Piemonte-C.Ticino (Svizzera)
3	Como	146	Lombardia
4	Trasimeno	128	Umbria
5	Bolsena	114,5	Lazio
6	Iseo	65	Lombardia
7	Varano	60	Puglia
8	Bracciano	57,5	Lazio
9	Lesina	51	Puglia
10	Lugano	50,5	Lombardia-C.Ticino (Svizzera