Rainbow darter, a type of fish, are caught by electrofishing, each fall and spring, at 13 sites both upstream and downstream of both the Waterloo and Kitchener WWTPs. Length, weight, sex, liver weight, and gonad weight data are collected. Male gonads are split and either stored for in vitro steroid analysis in the lab, or preserved for histological intersex analysis. Rainbow darter muscle tissue is used to determine stable carbon and nitrogen isotopic signatures, with and benthic invertebrates (hydropsychidae) as a food web baseline. At each site, water quality is also measured (nutrients, hormones, pharmaceuticals, water chemistry). This research involves both field and laboratory methods. All laboratory analysis will be done in the Aquatic Toxicology and Ecosystem Remediation Laboratory located at the University of Waterloo