1. Two hardwater eutrophic lakes of central Alberta were subjected to single doses of Ca(OH)2 (74 or 107 mg L–1). The effects of lime treatment on phosphorus (P) precipitation, sediment P release, and macrophyte biomass were assessed for up to 2 years.2. In both lakes, sediment P release was reduced to 16 and 27%, respectively, of pre‐treatment values by the first winter following treatment. However, sediment P release returned to pre‐treatment values during the following year.3. In contrast to these short‐term effects, macrophyte biomass decreased by as much as 80% after lime application and remained there for at least 2 years.4. Our results indicate that a single dose of Ca(OH)2 may give short‐term (< 1 year) control of P and long‐term control (> 1 year) of macrophytes in hardwater eutrophic lakes of Alberta.