Hydrogen peroxide (H2O2) is used as anti-parasitic veterinary medicine in salmon farms worldwide. In the period from 2009 to 2018 a total of 135 million kg of H2O2 was used in Norway, the world's largest producer of Atlantic salmon. Since the treatment water is discharged to the sea, concerns have been raised about effects of H2O2 on the coastal ecosystem. In the present study, Northern shrimp (Pandalus borealis) have been exposed to short pulses of H2O2 in the PARAMOVE® formulation, followed by a recovery period in clean seawater. The exposure concentrations represented 100, 1000 and 10 000 times dilutions of the prescribed treatment concentration for salmon; 15 mg/L, 1.5 mg/L and 0.15 mg/L H2O2. Significantly increased mortality was observed after 2 h exposure to 15 mg/L H2O2 (50%) and after 2 h exposure to 1.5 mg/L H2O2 on 3 consecutive days (33%), but no mortality was observed after 2 h exposure to 0.15 mg/L. The mortality occurred 2-4 days after the first pulse of exposure. The patterns of acute effects (immobility and death) could be captured with a toxicokinetic-toxicodynamic model (GUTS), which allows extrapolations to LC50s for constant exposure, or thresholds for effects given untested exposure profiles. Effects of H2O2 were also detected in shrimp that survived until the end of the recovery period. The feeding rate was 66% lower than in the control after 12 days of recovery for the three-pulse 1.5 mg/L exposure. Furthermore, dose dependent tissue damage was detected in the gills and evidence of lipid peroxidation in the hepatopancreas in shrimp exposed for 1 h to 1.5 mg/L and 15 mg/L and kept in recovery for 8 days. Fluorescence intensity in the hepatopancreas of treated shrimp increased 47% and 157% at 1.5 mg/L and 15 mg/L, respectively, compared to the control. Local hydrodynamic conditions will determine how fast the concentration of H2O2 will be diluted and how far it will be transported horizontally and vertically. Results from dispersion modelling (literature data) together with the current experiments indicate that treatment water with toxic concentrations of H2O2 (1.5 mg/L) could reach P. borealis living more than 1 km from a treated salmon farm.