It is the last two years that the amount of cooking fats in the sewer pipes in Ystad has increased.

From where and why the amount of cooking fat has increased, no one at the treatment plant knows.

- We do not have a real answer to that and we are trying to investigate.

We have not been able to see that there has been any change that can explain what we see now, says Sanna Nilsson, operations manager for the treatment plant in Ystad.

"An abnormal situation"

Last year, prosecution was brought in the Land and Environmental Court because the amount of cooking fat exceeded what was in the environmental permit.

However, the prosecution was dropped.

This year, the amount seems to be at the limit but still out of the ordinary.

- It looks better so far but is still an abnormal situation, says Sanna Nilsson.

Fat becomes raw food

- We can try to track where the fat comes from.

But the easiest thing is if everyone does the right thing from the start, says Sanna Nilsson.

When cooking oil, which is liquid, is flushed down the drain, it solidifies when it comes in contact with cold and forms lumps of fat.

The lumps of grease can cause flooding if they clog the drains.

But it can also cause other problems.

- There can be more problems with rats because they live in the pipe network.

The fat that accumulates there becomes like rat food and the rats can multiply.