Lake Erie is increasingly stressed by hazardous and nuisance algal blooms (HNABs) that occur each summer due to excess phosphorous (P) loadings from urban and, especially, agricultural sources. Building on an earlier economic analysis of the direct impacts of these HNABs, this study estimates the full economic impacts on the Ontario economy using a regional economic impact model. The full economic impacts include indirect and induced impacts in addition to the direct impacts associated with the costs previously reported in the literature. Province-wide, 3024 person years of employment are predicted to be lost on average annually in the period 2020–2024 if nothing is done to control phosphorus loadings to the lake. Employment losses are reduced by 812 person years (to 2212) if policy action is taken to control loadings. The equivalent figures for GDP are $147,351,000 and $38,431,000, respectively.