The redox processes that control Hg speciation in natural waters are poorly understood and study results often disagree, primarily a consequence of varied and often flawed methodologies. An incubation method was developed utilizing PFA Teflon® bag reaction vessels to reduce sources of error, and additions of isotopically labeled Hg to quantify rate constants. With low measures of error and duplicate bag reproducibility, this method was applied via incubations of natural waters in ambient sunlight to test three theories; 1) Hg oxidation and reduction are photochemically mediated, 2) Hg reduction is correlated to [DOC], and 3) Hg oxidation is enhanced by halides. The former was proven through the detection of redox chemistry during daylight and its absence in the dark. Results indicate the importance of both redox processes in natural waters, but failed to prove the latter two theories, potentially due to greater than expected [DOC] in one experiment.