The hyporheic zone is the ecotone between surface water and groundwater in streams. Organisms in the hyporheic zone can originate from both surface and groundwater habitats, but all major groups of animals found in freshwater have been found in the hyporheic zone. Because it creates interesting dynamics in the hyporheic zone, temperature is an important variable in studying hyporheic ecology. The hyporheos may also provide a thermal refugium for invertebrates and aid in maintaining and restoring thermal regimes of streams. These temperature dynamics underscore the importance of studying the hyporheic zone along a thermal gradient and in systems with unstable thermal regimes. Understanding the influence and role of temperature for hyporheic fauna is currently of great importance as anthropogenic impacts have modified global freshwater temperatures. Our study focuses on 11 streams around Iceland, with an emphasis on constant and variable thermal conditions. We sampled four lake-fed streams that have variable thermal conditions throughout the year and seven relatively thermally-stable spring-fed streams ranging from 2°C to 26°C. We collected surface samples and subsurface (hyporheic) samples from two depths. Early results show that invertebrate diversity and abundance decrease with depth.