Swimming pool disinfectants and disinfection by-products (DBPs) have been linked to human health effects (e.g., asthma and bladder cancer), but no studies have comprehensively identified DBPs in the water and determined their mutagenicity. Richardson et al. measured DBPs and disinfectant species in water from two public swimming pools in Barcelona, Spain, and assessed water samples using the Salmonella mutagenicity assay. The authors identified > 100 DBPs, including many nitrogen-containing DBPs that were likely formed through reactions with nitrogen from urine, sweat, and skin cells; many of these DBPs had not been reported previously in either swimming pool or drinking water. Bromoform levels were greater in water samples from the brominated pool than in those from the chlorinated pool, but many brominated DBPs were present in chlorinated pool water. Although chlorinated and brominated pool waters were both found to be mutagenic, mutagenic potencies were similar to those of drinking water. The authors note that the health effects of many DBPs are still unknown and suggest that DBPs that have not yet been identified may also contribute to the mutagenicity of pool water.