Blue-green algae form potential stromatolite structures in the Holocene subtidal Florida Backreef environment. The stromatolite structures are domal and circular to elliptical in plan view. The stromatolites occur randomly scattered among Thalassia sp. grass flats in about 3 m of water. The stromatolite structures are similar to many found in the Geologic record. Growth forms of the blue-green algae stromatolites ( Schizothrix ?) and their environmental occurrence are important when interpreting ancient depositional environments in terms of the water depth and relative position to the shoreline.