Identification of singlet oxygen photosensitizes in lambs drinking water in an alveld risk area in West Norway

► Lamb's drinking water in an alveld risk area contains potent photosensitizers. ► The amount of photosensitizers is at the highest at the outbreak of alveld. ► Analysis of lamb's drinking water can be important to predict outbreak of alveld. ► A wet and warm spring combined with high irradiance can trigger alveld outbreak.