Sampling date 06/2013. Scale bars indicate 25 µm.

Two images.

In 1977, Hoham & Mullet (https://doi.org/10.2216/i0031-8884-16-1-53.1) described cystozygotes of Chroomonas cryophila that appear very similar to the specimen shown above. They also described lipid accumulations at the poles of the cysts, which appear yellow, orange, or pink depending on sunlight exposure. According to Ettl (Ettl, H. (1983). Suesswasserflora von Mitteleuropa: Bd. 9.: Clorophyta I. Phytomonadina. VEB G. Fischer Verlag Jena), the sizes of the cystozygotes of Choroomonas cryophila found range between 10×16 µm and 21×37 µm; the size of my specimen was 24×41 µm, which is consistent with this range.
Matsuzaki et al. In 2019, (https://doi.org/10.1371/journal.pone.0210986) described two Chroomonas species whose cystozygotes also look very similar to the specimen.
I therefore assume that this is a cystozygote of a Chroomonas species.

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Place name: Wetland Torfmoos near Fieberbrunn (Austria) 
Latitude: 47.490431     Longitude: 12.557314

Microscope Zeiss Universal, camera Canon EOS 600D. DOF images.