Bonsoir tous
the 'foam-cakes' which can develop in fast flowing streams are a very interesting habitat for the so-called 'Ingoldian Fungi'.
Examples of some of the often distinctive conidia found can be seen here:
http://www.ascofrance.com/search_recolte/3964
http://www.ascofrance.com/search_recolte/3943
http://www.ascofrance.com/search_recolte/3010

Amongst these "aquatic hyphomycetes" one often sees diatoms and other algae, lepidopteran wing scales, pollen etc.; and also chance fungal spores from unknown fungi (which may or may not be aquatic in origin). Normally one ignores these, but occasionally one finds something so striking there may be a hope of getting an identification, even from a single spore. Here is an example of this and I am hoping that such a distinctive spore (which is surely an ascospore - Pleosporales or similar?) will be recognised by someone here. Notable are the large size of the spore and the very distinctive hyaline tips at each end (which are not formed within a single cell - the terminal cells are part-coloured). It may not be evident from the photograph, but the spore is 8-septate.

As ever any suggestions would be very welcome.

Chris