- An arrangement to increase (or decrease) the temperature in sea or lake water within a limited area. The arrangement is constituted by a basin (F, P1-P4, V1-V3, N1-N3 etc.) which is constructed and located in the sea water which temperature is desired increased. The basin shall primarily make the water circulation difficult between the basin and the outer sea so that a temperature difference is achieved, but it is not fully tight to allow a certain circulation. In one model (FIG. 1) the water circulation is uncontrolled with firm and statically arranged elements (YP1-YP3, HP1-HP7, E1-E10). In another model (FIG. 5) the elements of the basin (J1-E10). In another model (FIG. 5) the elements of the basin (J1-J3) are operated with regard to a temperature aimed at. Several more models (FIG. 8, FIG. 9, FIG. 12 etc.) are described.