El Maestrazgo is a karstic aquifer of more than 2,400 km 2 that occupies the northern half of the province of Castellón. Its main discharge area is in the coastal mountains of Irta. One of the most important springs in the system is the Font de Dins of Peñíscola, which is characterized by its fresh water channeled through preferential circulation channels without contact with sea water. After intense rainfall events, both on a local and regional scale, the usual hydrochemistry of these waters changes almost immediately and remains altered for days or weeks, being able to present stages of marked turbidity. This fact is due to the rapid influx to this upwelling of infiltrated waters in different sectors of the aquifer that significantly increase its flow. This article analyzes the cause-effect relationship of the turbidity peaks that sporadically occur in the Font de Dins spring with very intense or prolonged rains in the area. Once the relationship has been verified, a space-time study allows turbidity to be used as a natural tracer and to establish transit periods, groundwater flow velocities and recharge areas.