The paper gives results of a study of operational and environmental impacts of closed cooling systems, used for about a quarter of the nation's steam-electric generating capacity. Conclusions relating to operational impacts include: (1) closed cycle cooling leads to increased power plant heat rates relative to an open cycle cooling system, but is finding increased application at power plants in order to meet environmental or siting constraints (the wet cooling tower is the most often selected closed cycle cooling system); and (2) closed cycle cooling systems are more costly, in terms of both capital and annualized costs, than open cycle cooling (wet cooling towers are usually the least costly closed cycle cooling system, while dry cooling towers are the most expensive).