Algae are present in most fresh waters, including spring waters. Springs are the simplest of natural laboratories for studying interactions between a limited number of species and environmental factors, and they are refugia for a number of rare and declining species. This book provides information on the ecology and distribution of 174 abundant and common diatoms in spring waters and on 30 species that are poorly known and rarely reported. More than 2000 micrographs (including over 1000 SEM images) illustrate morphological characteristics of the species. The new genus Crenotia and three new species (Eunotia chelmickii, E. oligotraphenta and Staurophora lanceolata) are described and five new combinations are introduced. The species treated in this book were collected from 62 natural springs and five borehole-originated outflows characterized by heterogeneous geological, hydrological conditions; natural and affected by human impact (urbanization, agriculture). Diluted, calcium-rich but nutrient-poor, eutrophic, saline, carbonated or sulfide-rich springs were used as basis for the study. The key factors controlling species distribution in spring waters are thoroughly investigated and discussed. This book is a valuable source of information for biologists interested in bio-geographic diatom distribution and in the ecological effects of human interference and natural conditions on diatom distribution.