Bacterial mats (IMAGE) Max-Planck-Gesellschaft Caption A scuba diver observes the purple, white and green microbes covering rocks in Lake Huron’s Middle Island Sinkhole. Credit Phil Hartmeyer, NOAA Thunder Bay National Marine Sanctuary Usage Restrictions Usage permitted only in connection with the press release License Original content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.