Ebb and flood have lost their influence on the port in Greetsiel by the construction of the lock. Since 1991, the Sperrwerk Leysiel with Siel and lock has been the final construction of the dyke nose "Leyhörn", the core of the coastal protection measure Leybucht. The lock system ensures that the fishing and recreational craft fleet located in Greetsieler Hafen can reach the North Sea via the shipping channel and the reservoir, regardless of the ebb and flow.
The 30 meter wide Siel supports the drainage function of the plants in Greetsiel and Leybuchtsiel. The inland lake of 200 hectares of storage lake serves both to absorb the water draining through the river Siele and as storage space if inland water is pumped in via pumping stations in case of several-day storm tides.