It is forbidden to pour tea into the fish pond. Is there a grammatical error in this sentence? Should we say "It is forbidden to pour tea into the fish pond"

If you take it seriously, there is something wrong with it. Just a word, tea is forbidden to be poured into the fish pond. The word "bei" can be omitted, it just needs to be used for daily communication from time to time. Moreover, it seems that it should be a slogan, and it would be better to use an imperative sentence, so if you choose it, it means (you) prohibit or prohibit (you) from pouring tea into the fish pond.

I hope my answer can help you.