Forest harvesting can alter stream water quality with potential consequences for water resources and aquatic ecosystems. Much of our understanding on how harvesting impacts water quality is from small headwater catchments. We know less about the propagation of harvesting effects from headwaters to downstream reaches. We used data collected as part of an experimental harvest study at the Turkey Lakes Watershed, Ontario, Canada, to assess water quality response downstream of three harvested headwater catchments. Thirty years (15 pre- and 15 post-harvest years) of streamflow and water quality observations were made upstream and downstream of where the three harvested streams flow into a downstream reach. Some solutes, such as ammonium and phosphorus, did not exhibit a harvest response at the headwater or downstream reaches. Other solutes, such as silica and sulphate, showed a harvesting response at the headwater streams but no response at the downstream reach. Still other solutes, such as potassium, calcium, sodium, magnesium, chloride and dissolved organic carbon, showed harvesting responses at the headwater and downstream reaches, although the downstream responses were typically more muted and recovered to pre-harvest conditions more quickly compared to the corresponding headwater response. Our results highlight that downstream propagation of harvesting effects on stream water quality can persist for many years following harvesting but the magnitude of response, and thus downstream effects, depends on solute.