Characterization of iodine on-line using mixersettlers has been performed in reactor water, reactor water cleanup (RWCU) effluent, and condensate at the three boiling water reactor (BWR) nuclear power plants (F1, F2, and F3) at Forsmark, Sweden. Characterization of reactor water iodine has also been performed following reactor shutdown at F3. The dominating species in reactor water and condensate was iodide; the rest being essentially iodate. In RWCU effluent, the major species was iodate. Iodine isotopic ratios showed that iodate was delayed when passing the RWCU system. Formation of organic iodides in the RWCU system was not significant. No changes in the iodine species composition in the reactor water could be observed directly following reactor shutdown; however, iodide was with time slowly converted to iodate by radiation-induced oxidation. In reactor water <1% and in condensate and RWCU effluent up to 3% of the total iodine existed in the organic form. Organic iodides in the condensate were older than other iodine species.