Abstract: The invention relates to a cooling method and cooling system comprising a cooling device (1), in particular a cooling tower (1), for cooling cooling water and at least one consumer (4) to be cooled, wherein the cooling device (1) and the at least one consumer (4) are arranged in a cooling water circuit (1, 2, 3, 4), a filter (11) having immobilized microorganisms, in particular having a microorganism colony, being arranged in the cooling water circuit (1, 2, 3, 4) between the at least one consumer (4) and the cooling device (1) or in a separate circuit (1, 9, 10, 11, 12) connected thereto, in order to specifically filter out nutrients from the cooling water by means of metabolizing and/or storing the nutrients by the microorganisms in the filter (11), wherein the immobilized microorganisms are inoculated and cultivated outside the circuit with autochthonous and/or allochthonous microorganisms from the cooling system and are integrated into the cooling system as a functionally ready collection of microorganism