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Marine finfish aquaculture is a rapidly expanding industry and contributes significantly to global seafood production. However, this rapid growth raises concerns about its environmental impacts. In Greece, legislation on environmental monitoring of fish farms was implemented in 2019. These monitoring activities have resulted in a large-scale dataset on geochemical, sedimentological and macrofaunal parameters obtained from 106 fish farms in Greece. We use this dataset to detect overarching patterns regarding the spatial extent of the impact of fish farms on geochemical and ecological sediment parameters and to evaluate the modulating role of various environmental factors on the impact. Data were collected from 2019 to 2023 at 343 stations and analysed for geochemical and sedimentological (organic carbon, nitrogen, phosphorus, heavy metals, granulometry) and ecological (macrobenthic communities, ecological quality) parameters. Results show that organic and nutrient enrichment in sediments were detectable at least up to 130 m from the cage edges, while impacts on benthic macrofaunal indices were mostly limited to tens of meters. Sediment characteristics and geographic location were the main drivers for pollutant accumulation and benthic community responses, but the findings also underline the complexity of ecosystem responses and the importance of local conditions. We evaluate these findings with respect to monitoring practices and provide recommendations to improve environmental management and inform sustainable aquaculture practices.