A waste collecting system for collecting sunken waste from at least one aquaculture cage structure (1) positioned in a body of water (5), which cage structure comprises a collar (3) floating on a surface (4) of the body of water and an aquaculture cage (6) which is suspended from the collar. The waste collecting system comprises a waste receiving station and a pumping system (9) for pumping waste from the cage structure to the waste receiving station, which pumping system, for each of the cage structures, comprises: a suction head (10)； a conduit (11), running from the suction head to the waste receiving station； and an air injection device (13) connected to the suction head and/or the conduit for injecting air into the suction head and/or the conduit for creating an uplift in the conduit sufficient for a mixture of water and sunken waste accumulated at a bottom section (8) of the aquaculture cage to be sucked into the suction head and raised to the waste receiving station. The pumping system comprises, for at least one of the at least one cage structures, an air evacuation device (21) which is connected to the conduit for evacuating air, injected by the air injection device, from the conduit in order to prevent accumulation of stagnant air inside the conduit.
