The largest amount of zoo-and phytoplankton, fish eggs and fish fry inhabit the upper sea layers, usually the shelf area. Therefore, the influence of ship's cooling system on the marine biodiversity is considered. The intake of cooling sea water by ships and other marine technical objects occurs at a depth of about 10 m, the area where a great number of fish fry and fish eggs is concentrated. Thus, it has been shown that the plankton that gets to the cooling system during the intake of cooling sea water dies. An open-loop cooling system sucks in with outboard water these organisms, which, passing through filters, pipelines, fittings, etc., mostly perish under the mechanical and thermal influence. Existing filters and fish protection devices do not prevent this extermination; as a result, the biological productivity of seas decreases. In the paper the ways of solving this problem are proposed. The issues related to the implementation of the closed-loop cooling systems for power plants of the marine technical installations operating without consumption of outboard cooling water are considered. The implementation of such systems ensures high reliability and environmentally safe operation. Based on the results of the research, the examples of practical implementation of such systems are given. The issue related to the use of gas-liquid intensification of heat removal from sea water for closed-loop cooling systems of ship power plants is considered.