Between Ättekulla industrial area and Råån, there are two dams that collect water.

First the top pond was suspected, then the lower pond.

- In this situation, it is not at all likely that it is the ponds that affect fish death, says Lotta Wallin, group manager for environment and resources at NSVA, who leads the investigations at Råån.

What can be stated is that the fish death is due to a lack of oxygen in Råån, but what stems from the lack of oxygen is a mystery that eludes everyone involved.

- That there is a lack of oxygen is certain, but otherwise we do not know, says Lotta Wallin.

A tricky riddle

It may seem like a failure but it is apparently a difficult nut to crack.

- There are so many different criteria that can cause the death of fish.

We have no idea actually, says Lotta Wallin.

In the feature above, you will hear the next step in the investigation and what Lotta Wallin thinks may be behind it.