Matched chemical and ecological monitoring data were used to assess the effects of iron on benthic macroinvertebrate communities. Three measures of iron exposure: dissolved, total, and particulate iron were assessed. Ecological responses were normalised to an unimpacted reference condition to make site-specific predictions of the reference condition. Ecological data were expressed as an Ecological Quality Index (EQI), indicating quality relative to the reference condition. Quantile regression analysis was used to derive thresholds as an EQI value equivalent to the cut-off between good and moderate ecological status for water quality classification. Thresholds for Good Ecological Status ranged from 1.25 to 2.46 mg L⁻¹ depending on the measure of exposure and ecological response.