Eunotia fennica (Hustedt) Lange-Bertalot, originally described as E. denticulata var. fennica Hustedt, was identified in good numbers from a small Orchid Bog Pond, Newfoundland. We investigate the population and valve morphological structure of this taxon using LM and SEM preparations. Additional specimens representing the Eunotia denticulata-complex are identified from five regions across eastern and northern North America and are compared with E. fennica. Current problems in the taxonomy of the E. denticulata complex are explored through an investigation of the original descriptions, and characters used to separate E. denticulata, E. neoborealis and E. fennica are identified. A preliminary examination of water chemistry is also made and related to the taxa. This Orchid Bog Pond is an acidic, poorly buffered, dilute waterbody situated on a sphagnum bog with a selective diatom flora which includes a good population of E. fennica, a taxon presently identified across three continents.