A new toxin producing freshwater Limnothrix from Central Queensland, Australia has been detected. The features of this cyanobacterium in both field and pure cultures were consistent with the cyanobacterial species Geitlerinema unigranulatum (R.N. Singh) Komárek and Azevedo and Geitlerinema amphibium (Agardh ex Gomont) Anagnostidis as well as with the earlier Australian descriptions of Limnothrix cf. planctonica Baker and Fabbro. However, genetic analyses closely group this cyanobacterium with the commonly occurring temperate species Limnothrix redekei (Van Goor) Meffert. The Limnothrix may occur as solitary planktonic trichomes, mats on the bottom or within the water column, or in balls floating on the surface. A fine mucilage often confused with a sheath may cover older trichomes. The long, thin trichomes may glide into coils, may flex and are not attenuated at the ends. The cylindrical cells are 1.6-2.0 μm wide and 5.0-6.5 μm long. Constriction at the cross walls is generally not observed and cross walls are often indistinct. Refractile granules are present in the cells, - near the cell walls and sometimes distributed within the cells. A new species of straight Sphaerospermopsis closely aligning with Sphaerospermopsis reniforme (Forti) Zapomĕlová, Jezberová, Hrouzek, Hisem, Rĕháková et Komárková comb. nov. has also been detected. Trichomes are normally solitary, straight or slightly curved often with a metameric structure. Trichhome are found with or without heterocytes and may be constricted at the cross walls. Vegetative cells are 2.5 to 4.9 µm wide and 4.0 to 10.4 µm long. Heterocytes are ovate to sub-cylindrical 3.0 to 3.6 µm wide and 6.8 to 10.3 µm long. The cell contents have aerotopes and the apical cells are tapered or bluntly rounded.