[4] They are found in France,[5] Italy,[4] Germany,[6] Switzerland,[7] Austria,[8] Slovenia,[9] Serbia,[10] the Netherlands,[11] Belgium,[12] Hungary,[13] Croatia,[13] Albania,[4] Bulgaria,[4] and Bosnia and Herzegovina.

[4] It was previously thought to be a single species based on morphological characteristics, however genetic and genomic research has revealed additional diversity within G. fossarum.

[16] Gammarus fossarum prefer flowing, well-oxygenated water and are often found in smaller and mid-sized streams, particularly in hilly and mountainous areas.

They are known for their shredding of leaf litter detritus that enters streams and waterways from the surrounding forest, but G. fossarum also feed on other macroinvertebrates.

Their survival,[24] growth,[25] reproduction,[26] activity levels,[1] physiology,[1] and food consumption[27] are used as indicators of environmental conditions, including acidity,[27] nanoparticles,[1] wastewater effluent,[26] pesticides,[24] and pharmaceuticals.