The water quality of forest brooks was monitored after manual clearing of forest plantations and in an area treated with glyphosate for two consecutive years. In both cases an increase in the concentration of NO3−was evident. Manual clearing gave concentrations of 20–60 μM NO3−during winter and less than 10 μM during the growth season, which is in the same range as usually found in glyphosate‐treated forests. The doubly‐treated glyphosate area showed increased leaching of NO3−during summer, giving 30–60 μM NO3−as the maximum value the first summer after the second application. The summer leaching decreased the following two years, giving brook water with 5–25 μM NO3−. No effect of the treatments was found for the other nutrients measured. Both manual clearing and glyphosate application in forest plantations give the same small effect on brook water quality. The effects appear not to be of ecological importance.