The images show a Cladophora-like mat that forms a biofilm in a brine RO system. The sample was collected from cartridge filters processing 1.4% brine. The filament branching is typical of Cladophora, as are the cell length to diameter ratios, but the overall cell sizes are smaller than those for freshwater Cladophora. The biofilm occurs as a thick white to yellowish exudate.