AbstractThe paper focuses on the definition of the vulnerability of phreatic waters to surface water pollution. The amplification of water exchanges between surface and underground waters, because of human activities, is considered as a risk of contamination of aquifers. The aim of this paper is to present a first synthesis of oligochaetes as biological describers of these exchanges.Field investigations have shown that several rare and/or stygophilous taxa are found in surface (coarse) sediments of rivers upstream and/or downstream of dams or gravel operations. These observations relate to species such asPropappus volki, Pristinaspp.,Chaetogaster parvus, Rhyacodrilus carsticus, R. falciformis, Phallodrilusspp. The data suggest that these species invade surface waters from phreatic or interstitial waters when water flows are amplified between the two. Flow amplification is considered as a consequence of dams' and gravel operations' hydraulic impact. But the lack of hydraulic validation of the presumed active exchanges describer's (AED) ecological status given to those species remains a problem, giving the opportunity to examine the link between hydraulics and biology.Preliminary results on two gravel pits of La Wantzenau (Rhine alluvial valley, France) have shown relations between the distribution of oligochaetes, especially Lumbriculidae, and soil filtration properties. Two other studies were planned along an industrially polluted tract of the River Rhǒne (Grand Gravier Island). Horizontal and vertical zonation of the river banks were performed by studying simultaneously hydraulics and oligochaetes. Preliminary results have shown that the absolute and relative abundances of taxa such asPhallodrilussp. andS. velutinusincrease in relation to the permeability of superficial coarse substrate in the horizontal plane, and to the current velocity in underground porous media in the vertical plane. The increasing percentages ofP. barbatusand the decreasing percentages of Tubificidae reveal active exchange zones where superficial waters are renewed by groundwaters. Some other species such asP. vejdovskyiseem to be potential describers of water exchanges