To me these are typical Sciaridae larvae and pupa. Presumably they are accidental inhabitants of the lake, as the family is entirely terrestrial (as far as I know).
Oh! ok. ... I found that some of its can live in tussocks in lake's shore... it's fit with our sample (juncus zone) - in Darold Batzer & Dani Boix.
Invertebrates in Freshwater Wetlands: An International Perspective on their Ecology. 2016. Springer Ed .