As part of the on-going monthly monitoring we wanted to better understand the diversity and variability of organisms within each stream. The focus is on the attached algal communities covering the rocks, which are made up mainly of single-celled diatoms. Diatoms are highly sensitive to changes in their environment, such as the concentration of nitrogen and phosphorus within the streams, as well as water depth and velocity. Diatom communities reflect the localized environment where they are found within the stream. In order to characterize within-reach variability in diatom communities, a one day field sampling campaign was undertaken at Newby End Farm, in the Newby Catchment, in October 2011. Quadrats were placed across the stream, and cobbles were selected from within each quadrat. These cobbles where scraped using a toothbrush and the resulting samples were brought back to the laboratory for microscopic analysis. Alongside the diatom samples, water depth, velocity and turbidity were recorded, together with chemical measurements such as pH and dissolved oxygen, in order to try to understand what controls the diatom communities found within the streams. Few studies have examined habitat and community diversity at this fine spatial scale and we expect the results to better inform our biomonitoring.