Broad-scale impacts of salmon farms on temperate macroalgal assemblages on rocky reefs

•Nutrient impacts on benthic algae were investigated along gradients from fish farms.•Detectable impacts extended between 100m and 400m distance from farms, on average.•Macroalgal assemblages near farms were overgrown by epiphytes.•Canopy-forming algae appeared unaffected by the organic richness gradient.