Unlike chlorine, chloramines do not dissipate rapidly from water, so you will have to take steps to remove them. Chloramines are a combination of chlorine and ammonia, both of which are toxic to fish. As chloramines break down, either naturally or through the use of dechlorination chemicals, ammonia is freed up. This ammonia can be removed from fish tanks or ponds by using commercial products available at pet supply stores. Biological filters, natural zeolites and pH control methods are also effective in reducing the toxic effects of ammonia.
Chloramines affect saltwater fish in the same way they affect freshwater fish.
Koi are just as susceptible to chloramines as other fish. Unlike chlorine, which dissipates when water sits for a few days, chloramines may take weeks to disappear. To know for sure, you'll have to monitor for total chlorine residual. A free chlorine test of chloraminated water would read zero but still be toxic to fish. To be effective, however, it must contain high quality granular activated carbon and you must permit sufficient contact time between the water and the carbon.