A tracer test during low-flow conditions was carried out in the karstic aquifer of Sierra de las Nieves
(Málaga) in order to assess its hydrogeological functioning and vulnerability to contamination. Two
kilogrammes of Eosine were injected in an active siphon located in the Sima del Aire cave shaft (-640 m)
at the end of August 2003. The springs were sampled until November 2003. For more than 50 days, the
tracer was not detected at any of the springs. After several rainfall events in October 2003, a signal was
observed in the two Río Grande springs. The first arrival of Eosine appears before the increase of spring
discharge and the dilution effect of the most important rainfalls (86 mm, October 25th). The calculated
groundwater velocities (below 4 m/hour) are not representative of the dry period because rainfall forced
the Eosine transport. However, they give an idea about the long residence time if a contamination event
occurs during low-flow conditions