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The triangular shaped thorax indeed suggests Limnophorini.

This fly was observed at an altitude of 1800 m or so near a mountain stream. So Limnophorini would make sense as Limnophorini tend to be close to water.

I think Villeneuvia, Neolimnophora, and Limnophora an be ruled out

Not sure if this can be Lispe.

I wonder how Spilogona acrostichalis, aerea, alpica, micans, sororcula or triangulifera looks like, which should occur in the Alps in Austria. Especially the triangulifera name would fit this animal.