Diatoms of the Clark Fork River

When you wade into the Clark Fork River in the summer you will most likely slip on the rocks because of benthic diatoms and the mucilaginous excretions they use to adhere to the substrate. Diatoms are microscopic, jewellike, single-celled algae with silica cell walls. They possess characteristics of both plants and animals, such as photosynthesis and directed motility. Diatoms are the base of the aquatic food chain, but they can also be harmful, producing powerful neurotoxins that contaminate crustaceans, bivalves and fish in the oceans and also the massive stalk growths of Rock Snot (Didymosphenia geminata) that choke out other aquatic life in some rivers and streams. Diatoms are good indicators of water quality and have been used to monitor the health of the watersheds of Montana since the 1970s. As an example, assessments were made of diatoms in the Clark Fork River upstream and downstream of the Frenchtown pulp mill in 2005, 2007 and 2009. These assessments suggest that there is some impairment of beneficial uses due to excess nutrients, and this assessment did not change over the sampling period. Examples are presented of diatoms common to the middle Clark Fork and considered indicative of various water quality conditions