Two weeks ago all the fish in the Vege river were killed, following a leak of "organic oxygen-absorbing" material from a nearby Findus pea processing plant, local newspaper Helsingborgs Dagbladet reports. The pea-processing plant has been closed since the first incident.
But on Sunday police were called to the Boserup stream, and found a similar scene.
Findus say the nearby factory has no direct waste outlets into that waterway, but one theory is that waste water from the plant used to irrigate nearby farmlands may have leaked into the stream, and it may have contained the same material as in the previous incident. The fish may then have suffocated to death.
Water samples and dead fish have now been collected to try to find out the cause of the mass extinction.
Local newspaper Helsingborgs Dagbladet says thousands of fish have been killed in the latest incident.