Lough Ree, which is about 25 km long and 7 km wide, lies entirely on Carboniferous Limestone. While it shows some evidence of being a solution lake such as undercut rocks (1), the existence and orientation of the deep areas of the lake are consistent with an origin by ice erosion

The lake has a very irregular shoreline with extensive reed beds and an uneven bottom. There are many sizeable islands particularly in the upper area. The greater part of the lake is shallow and less than 6 m deep, however, there are a number of deep trenches running in a north-south direction with a maximum sounding of 35 m near the middle of the lake. The catchment (Fig. 1) has a low population density. The areas west and north of the lake have a population density of less than 20 persons km-2 according to the 1981 census data. There are five towns in the catchment with populations between 1000 and 5000 people but none are likely to have any effect on the lake in terms of effluent discharge.

Agriculture is the main activity in the catchment and there are extensive peat-mining activities just north of the lake. The peat is used largely for the generation of electricity. There are several small agri-industry plants in the catchment and light and electronic engineering, chemical and coal mining industries are significant employers.

Lough Ree is the second largest lake in the River Shannon System after Lough Derg. It forms part of the Shannon Navigation System and its development as an amenity and recreational area for cruising is its principal beneficial use. It is also renowned as a game and coarse fishery holding excellent stocks of several species of coarse fish. The water supply for Athlone (popul. 14,000), the principal town of the region, is taken from the lake outlet, the River Shannon.

A detailed investigation of the water quality of Lough Ree and its feeder streams was carried out in the period 1979-1981, with updates in 1984 and 1986 (Bowman, in prep.). An initial assessment indicates that the lake was not significantly affected by artificial eutrophication in the 1979 1981 period. However, a light increase in the level of algal production was noted in the subsequent examinations. The values recorded for chlorophyll a and the total phosphorus concentrations place the lake in the border between mesotrophic and eutrophic categories according to the O.E.C.D. scheme (R).