The investigation of environment indicators is a descriptive approach but it has the advantage of leading fairly rapidly to practical conclusions. We present the results of an application to two Alpine lakes - Annecy and Le Bourget. It is based on a comparison of hydrobiological parameters and socioeconomic data. The comparative study of the two lakes leads to a global view in which the purity of the water is of great importance. We demonstrate that it is possible to judge it according to two hydrobiological variables - the colour and turbidness of the water. To go further than this one must distinguish between the various functions of the water. There may be incompatibilities between them which poses the problem of spacial distribution and hence of planning. In practical terms we have built four particular functions (sport, ecology, its ludico-social function and its visual function). For each we propose particular indicators.
