A. This slippery coating is caused by the secretions of the literally billions of single-celled algae called diatoms found wherever there is adequate light and nutrients. The technical name for this community, including the associated protozoans, bacteria, fungi, and detritus, is periphyton. This community is one of the two major food bases for aquatic organisms (the other is fine particulate organic matter) and is the primary contributor to dissolved oxygen in the water. Each cell is composed of two pure silica (glass) halves which fit together like a pill-box. The patterns of these cases are marked by various striations and patterns, and are quite beautiful when viewed under a microscope. They are the river and stream equivalent of phytoplankton, the so-called "grasses of the sea." ~ Stream Doctor

The 'Stream Doctor' is a retired professional stream ecologist and author, now living in the West and spending way too much time fly-fishing. You are invited to submit questions relating to stream-ecology directly to him for use in this Q & A Feature at streamdoctor@aol.com. Please include your name and town.