One still works: every water mill has an upstream stream - in the case of the Vierrademühle, that's the Oberbach, and a downstream stream, that's the Tollense. The Ölmühlenbach with the weir is still used today to regulate the Tollensesee - that is the huge "mill pond" of the Vierrademühle. Because there was always enough water, the four-wheel mill was able to develop into one of the largest mills in the north. But it can be bigger: The Great Mill in Gdańsk had up to 18 wheels!
There is more to report: The Oberbach and an earth dam were built right after the city was founded in the 13th century to dam up the lake by 1.5 - 2 m. What a major project of our ancestors! The earth dam can still be seen today in the Brodaer Strand area. Below (north) there is and is a deeper fracture through which the Tollense flows. What did you achieve with the traffic jam? (1) the mill received enough water level = energy, (2) the area around the young town was artificially swamped, which improved its defense capability and (3) the town's opponent, the old Slavic settlement center in the south of Lake Tollense (Rethra?), put under water. It just flooded and people moved away. You can find the remains today in the Lieps 1/2 to 1 m under water. The Christian colonizers were not squeamish about asserting themselves against the old population. Is that all true? At least I didn't think it up myself.
And one more thing: the four-wheel mill used to stand on an island. The outflow of the city moat led (unlike the Lindebach today) around the back of the mill into the Tollense. The mill was fortified and part of the defense system. Exciting?
At the Ölmühlenbach there is another mill stream that leads to another mill before the weir. It stood opposite today's Uthoff fish farm on a kind of island. Today there is a horse pasture, but with enough imagination you can still "see" it. However, I really don't know what's behind the term "oil mill".
You can also take a look at the water supply of the Lohmühle. It had 2 storage ponds - one is the swan pond, the other was in the area of the weir south of the Ziegelbergstrasse. No comparison to the Tollensesee!
By the way: My grandfather was a master mill builder ...