Invasive crayfish exert adverse impacts on native biodiversity in Europe. This field study investigated the scope for use of electric shock treatment to eradicate signal crayfish in a small headwater stream.High intensity (96 kW, direct current 1600 V, 57.8 A, at 7 Hz) repeated shocks were delivered via electrode tapes to two sections of stream. Both had 98 min as 2-min shocks. Section 2 had additional 15-min shocks to a total of 308 min.Crayfish mortality was 86% and 97% in the two sections respectively, based on the number recovered when the channel was subsequently dewatered. The survivors found were in the banks. Mark–recapture indicated that 72% of the total population was captured, hence the minimum mortality was 77% of the total population after the longer treatment.All sizes of crayfish were affected, but small individuals (<30 mm carapace length) were more susceptible.Test cages showed increasing mortality with exposure. A fitted model showed 50% mortality with 17 min shock time, 75% mortality with 30 min (distance to electrode in the range 10–50 cm).The treatment is a possible non-selective method of control for invasive crayfish in small watercourses, rather than an eradication method, because some crayfish survived in the stony banks. Periodic treatment downstream of a physical barrier would potentially keep the crayfish density low and may therefore reduce the risk of the barrier being overcome by upstream invasion. Options for further investigation to improve the method are discussed. Copyright © 2014 John Wiley & Sons, Ltd.