"One is not supposed to swim here."
Translation:Man soll hier nicht schwimmen.
I've noticed that a lot of modal verbs are followed by "nicht", rather than how "nicht" normally comes before the verb. I took this to be the equivalent of English can't (kann nicht), shouldn't (soll nicht), etc. But in this sentence, nicht cannot come after soll; it is marked wrong. Does anyone know the rule for this?
I think it's more a case of nicht/"not" being next to the full verb in both languages, don't you think?
The tendency in German is for it to go toward the end of the sentence when negating the full verb. Since there are so many possible sentence constructions there's no fixed rule - just a combination of tendencies. You can read more about it on Canoo.net.
That link was down for me, but I had good luck with the "German is Easy!" blog: https://yourdailygerman.com/position-nicht-german/