There are over 40,000 chemical compounds registered for use in Australia; however, very few of these have been monitored in aquatic receiving environments. Furthermore, their toxicological effects on fish species in Australia are largely unknown. Studies on trace organic contaminants (TrOCs) and endocrine active compounds (EACs) in Australia have focused on wastewater effluents, and limited knowledge exists regarding the relative contribution of different potential sources of TrOCs and EACs to the aquatic environment (e.g. pesticide run off, animal farming operations, urban stormwater, industrial inputs). This study combined chemical, in vitro, in vivo and in situ techniques to determine the extent of endocrine disruption in fish living in 73 rivers across mainland Australia. These rivers were sampled quarterly for one year to determine the chemical concentrations of 56 compounds including 42 TrOCs and 14 EACs. Monitored chemicals include: 30 pharmaceuticals, 4 personal care products, 3 industrial compounds, 7 pesticides, 10 natural hormones and 2 synthetic hormones. At least one of the 56 compounds was detected in 99% (281 of 285) of grab river water samples. On average five compounds were detected per sample, with a median of four and a maximum of 21 compounds per sample. [...]