Iceland is one of the countries with the highest freshwater availability according to UNEP's Vital water graphics (http://www.eoearth.org/view/article/152861/). Additionally, being an island, it is rich in coastal brackish and saline aquatic habitats. However, little is known about the microcrustaceans and rotifers inhabiting these numerous habitats. The freshwater fauna of Iceland is relatively understudied compared to the fauna of adjacent marine ecosystems. Exhaustive sampling of deep-sea fauna was conducted within the inter-Nordic BIOICE project. As a result, Apostolov (2011) recorded 32 copepod harpacticoids of which 20 are new for the fauna of Iceland. The first data on freshwater microinvertebrate fauna of Iceland date back to the 19th century (Guerne and Richard 1892a, Guerne and Richard 1892b). The first study on the rotifer fauna from the middle of the 20th century listed 59 species or subspecies (Bartos 1951). The majority of the available studies on inland water bodies focused on large lakes: Mývatn in the north-east (Ornolfsd and Einarsson 2004, Adalsteinsson 1979, Jonasson 1979, Lindegaard 1979); and Thingvallavatn (Antonsson 1992) and Kerið Lakes (Evtimova et al. 2014) in the south-west of the country. Recently scientists have become increasingly interested in the inland freshwater copepods and cladocerans from small freshwater bodies (Novichkova et al. 2014, Scher et al. 2000). Data on observed morphological variability and teratology of lower crustacean in subpolar environments, including Iceland, were presented by Sinev et al. (2012), Pandourski and Evtimova (2009), Pandourski and Evtimova (2006), Pandourski and Evtimova (2005). These aberrations affected the fifth pair of legs in calanoids, the posterior part of the body in cyclopoids, or the head and antennule in cladocerans. Our study presents data on taxa composition of Rotifera, Cladocera, and Copepoda in various aquatic habitats from South-western Iceland, including marine interstitial, wet bryophytes, springs, brackish and freshwater ponds and lakes.