I thought this was the procedure. I'm not sure how to report it from here at this point until I see the sentence again.
The procedure is always to report in loco when you see the sentence - if you're unsure, send a report anyway (the creators will get our reports in bulk when they log into their special software, but you need to report them the right way).
I put, "The water-level is very high", and Duo told me that I was nearly correct. They gave the "correct" answer as: "The water_level is very high". I have reported it.