The Bothnian Sea which is located between Finland and Sweden represents an important source of fresh water to the Baltic Sea. We here present new data on the radioactive isotope I-129 species from water samples collected in December 2009 at different depths in the Bothnian Sea. Concentrations of I-129(-) (iodide) in the Bothnian Sea range from 14 x 10(8) to 32 x 10(8) atoms/L, while (IO3)-I-129 (-) (iodate) concentrations are relatively low and fluctuating at 1 x 10(8) atoms/L. For nutrients data determined in the same samples as I-129, significant correlations could be found between I-129(-) and total P, NO3-N, SiO3-Si, but rather poor with NH4-N. The correlations suggest comparable source pathway of I-129(-) and nutrient parameters, while the source of NH4-N may be different. The small amounts and negligible change of (IO3)-I-129 (-) indicate prevailing extensive reduction of iodate in the Baltic Sea.