A biocide is formed by mixing at least one of ammonium sulfamate and ammonium carbamate with an aqueous solution of a hypochlorite oxidant at a molar ratio of ammonium to hypochlorite of at least 1:1. The biocide is useful in treating microbial or biofilm growth, pulp and paper process water, cooling tower water, waste water, reclaimed waste water, sludge, colloidal suspensions, irrigation water or a medium having a reducing capacity.