West Thumb Geyser Basin on the shore of Yellowstone Lake
West Thumb Geyser Basin is one of the smallest geyser basins in Yellowstone yet its location along the shore of Yellow-stone Lake ranks it as the most scenic. West Thumb has less geyser activity than other basins. But West Thumb, for its size, has it all-hot springs, pools, mud pots, fumaroles and lake shore geysers.
Since the mid 1970s, West Thumb has decreased in thermal activity. Some temperatures have cooled in the basin allowing large colonies of algae and cyanobacteria to grow. As a result, large newly-formed microbial mats flourish on the run-off channels and along the edges of pools.