Is it allowed to build a public road through private property?

Hello everyone!
We have the opportunity to purchase a plot of land cheaply. However, a public canal runs right through the property. Nevertheless, the building area is large enough to build on. The plot is shaped somewhat like a "bathtub," and I would like to know whether it is possible to fill in to make the land reasonably level. My father-in-law says that filling in is not allowed due to the canal. Is that correct?

Regards
J.

My father-in-law says that due to the canal, filling is not allowed.

What does the development plan say about fillings? Photos or plans are very helpful for the answer, by the way!

My father-in-law says that you are not allowed to fill up because of the sewer. Is that correct?

The building authority and the municipal drainage services can answer that best, but my experience with a plot we once were interested in, which also had a sewer underneath, is that you are not allowed to build structures (garage, garden shed, etc.) over it. In case you build a terrace over it, it depends on what is agreed upon. In the worst case, the city will dig up the ground if they need to access the sewer and only refill the hole afterward. You would then have to repair the terrace yourself. However, it is not clear to me why you should not fill up JUST BECAUSE of the sewer. If, for example, it is only about 30cm more or less, it probably does not matter when digging. Filling up is more a matter of terrain modeling and thus independent of a sewer, but rather a matter of the development plan.