The beaches of Sant Pere Pescador are part of an extensive littoral bar whose inner edge formerly coincided with the area where different river arms of the Ter and Fluvià joined and flowed. Remnants of wetlands, depressions, and former floodplains are still preserved from that landscape, helping to explain the uniqueness of this stretch of coast. The dynamics of the sand are strongly influenced by the wind.

North-westerly winds predominate, especially the Tramontana, though thermal winds, much appreciated by kitesurfers and windsurfers, and southerly wind episodes also play a part.

When an intense and prolonged tramontana wind occurs for more than a day, large quantities of dry sand can be mobilised and transverse dunes can form, which are spectacular. If the wind directions subsequently change, these dunes can evolve into more complex, barchan-like shapes.

This landscape, however, is extremely dynamic. A sufficiently intense winter storm can erode or even completely wipe out the dune system formed during the preceding months. The sand mobilised by the surf is redeposited onto the beach and, when it dries, is once again exposed to the action of the Tramuntana. Thus, the cycle of transport, accumulation, and formation of new dunes restarts.

This interplay of wind, swell, humidity, and sand creates a system of ephemeral dunes, constantly transforming. It is precisely this mobility, capable of building and erasing the landscape in a matter of weeks, that makes the beaches of Sant Pere Pescador a particularly unique coastal environment.