Abstract The fate of triclopyr butoxyethyl ester was investigated following direct aerial application to a boreal forest stream. The average deposit monitored at the stream surface was 3.67 kg acid equivalent (a.e.)/ha (range = 3.35-3.99 kg a.e./ha). Residues of triclopyr as the butoxyethyl ester (TBEE), triclopyr acid (TRI) and pyridinol metabolite (PYR) were determined in various aquatic substrates. Streamwater residues of TBEE resulting from direct overspray were characterized by instantaneous maxima (0.23-0.35 mg/L). A series of diminishing pulses of chemical associated with inputs upstream of the sampling site were observed. Average concentrations of TBEE in stream water ranged from 0.05 to 0.11 mg/L during the first 12 to 14 h post-application and declined to levels below the limits of quantification (0.001 mg/L) within 72 h post-application. Transient residues of TRI were observed in stream water, with a maximum concentration (0.14 mg/L) 6 h post-application. The PYR residues did not exceed limits of quantification (0.05 mg/L) in any sample. Results indicate that natural dissipation mechanisms reduce both the period and the concentrations to which aquatic organisms would be exposed.