Figure 2. ROV image of sediment surface of the deep, aphotic Isolated Sinkhole showing the brown and grey mats and a near-bottom nepheloid layer (Biddanda et al., 2006). Left Panel: ROV-video still images of conspicuous benthic grayish-white and brown mats, composition unknown; Right Panel: ROV image of sediments and exposed logs in Isolated Sinkhole (93 meters). Also in the photo is a cloudy nepheloid layer about 1 meter above the lake bottom – presumably caused by venting groundwater at the site – as indicated by water chemistry. Image courtesy of Thunder Bay Sinkholes 2008.