This file is from Wikimedia Commons and may be used by other projects.
The description on its file description page there is shown below.
Summary
DescriptionCyanobacteriaColl1.jpg
English: These "jelly balls" are colonies of the cyanobacteria species Nostoc pruniforme ("Mare's eggs"), living in freshwater ponds. (Determination was microscopically confirmed by Professor Dr Ludwig Kies, Hamburg.) Note: Many other single-(or few-)celled organisms also form gelatinous colonies in spherules. A reliable determination is only possible by microscope! The shown species is rather rare today and indicates clean water. Furthermore, my impression is that the trivial name "Mare's eggs" is not exclusively related to the concrete species Nostoc pruniforme, but also used for diverse different spherule algae (?).
Deutsch: Teichpflaumen, bei diesen gallertigen Kugeln handelt es sich um Kolonien der als Nostoc pruniforme bestimmten Süßwasser-Cyanobakterien (oder: "Blaualgen"). Vielen Dank an Prof. Dr. Ludwig Kies, Hamburg, für die mikroskopische Nachbestimmung! Beachte: Sehr viele andere ein-/wenigzellige Organismen formen ebenfalls gallertige Kolonien in Kugelform. Eine sichere Bestimmung ist normalerweise nur per Mikroskop möglich! Die hier gezeigte Art ist heutzutage nur noch selten zu finden.
Date
Source
Own work (collage of 4 pictures). Location (partially ex situ): North-eastern Lower Saxony, Germany.
to share – to copy, distribute and transmit the work
to remix – to adapt the work
Under the following conditions:
attribution – You must give appropriate credit, provide a link to the license, and indicate if changes were made. You may do so in any reasonable manner, but not in any way that suggests the licensor endorses you or your use.
share alike – If you remix, transform, or build upon the material, you must distribute your contributions under the same or compatible license as the original.