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According to Brauns "Puppen terricoler Dipteren-larven" they may be Cecidomyiidae or Lycoriidae (=Sciaridae) because they have protuding acute horns (lateral view). Then they are not aquatic but accidently fallen in water. This is the only idea. Possibly something else............:| Tanyderidae?
Possibly wing venation may help. It is not clear from the photo where the real veins are and where the folds.