Eighteen primarily lowland stream segments were sampled along the coast of French Guiana in South America. Streams varied from small rivulets to larger streams (< 2-20 m width) with substrata ranging from sand and gravel to large boulders. Waters were warm (24-25ºC), acidic to neutral pH (4.6-6.9) and low ion content (10-60 μS·cm–1). Mean species number per stream segment was 4.2 and ranged from 1-10. From the 75 samples collected, 26 infrageneric taxa were identified as follows: 9 Cyanobacteria, 4 Chlorophyta, 3 Heterokontophyta and 10 Rhodophyta. The rhodophytes were not only the most species rich, but also the most dominant in percent cover. The genus Batrachospermum was represented by eight taxa. Batrachospermum section Contorta was the most species rich with B. ambiguum, B. gracillimum, B. guyanense, B. intortum and B. nodiflorum, with each collected from one to two locations. In contrast, only two species from section Aristata, B. cayennense and B. macrosporum, were identified, but gametophytes were collected in eight and six locations, respectively. From section Turfosa, B. turfosum, a taxon typical of brown water streams, was present in three of the streams surveyed. Compsopogon coeruleus was collected from two locations. A rarely reported taxon, Ptilothamnion richardsii, was discovered as an epiphyte on aquatic macrophytes in one stream and on B. turfosum in another.