Managing eutrophication depends on reducing nutrient inputs into watersheds. Point sources can be regulated through management agencies, and non-point sources can be regulated through the promotion of practices that use fewer nutrients. For instance, Horrigan et al. (2002) propose a large-scale shift to sustainable, organic agriculture that does not rely on artificial fertilizer. A simpler but less comprehensive strategy would be to apply fertilizer more carefully so that fewer nutrients end up as runoff.
Image source: http://www.greenista.com/tag/gardening/