Boulders and pebbles in creek bed are covered with a slippery film of microbial material. A fluorescent light view of the microbial felt. In Figures 7 and 8 we see the effect of lower flow velocity. Low relief mat covers boulders and sediment in swiftly flowing water. Darker spots are areas with higher diatom abundance.
Dark color indicates abundant diatoms within the blue-green algal felt.
At somewhat slower flow vertical pinnacles form. These are buoyed by gas bubbles, but also firm enough to stand up without being buoyed. Darker colors indicate increased diatom abundance. Abundant pinnacles of blue-green algae and diatoms in calmer water. Gas bubbles provide buoyancy.