Phycology, a sub-topic of botany, is the academic discipline involving the study of algae. Phycologists, scientists who study algae, tend to be specialize in either diatoms or soft algae, and they tend to further distinguish their studies as either involving marine algae (those living in salt water) or fresh-water algae.
There are many algal taxa; estimates are that as many as 200,000 distinct species may exist, although only a fraction have yet been identified. In the 1940's, diatoms began to be studied for ecological assessment by Dr. Ruth Patrick of the Academy of Natural Sciences Philadelphia. Since algae live in a wide variety of habitats and have specific ecological requirements, the mix of species found in water samples can be an indicator of water quality. Such studies are complex and involve many factors, such as where and when the sampling occurs, how the counting of species is done, and how the data is afterward analyzed. Algal assessment is practiced in modern times by the U.S. Geological Survey and by many state Environmental Protection Agencies.
The study of algal fossils found in sediment cores from lakes and streams is useful in paleolimnology, a field of study concerned with studying the history of inland waters (lakes and streams; freshwater, brackish, or saline), especially climate change and the impact of human activities upon the overall health of water bodies.
In autumn of 2008, the 20th International Diatom Symposium (IDS) was held in Dubrovnik, Croatia and attended by around 200 people. This symposium, which occurs every two years, is a key opportunity for exchange among the relatively few world experts in Phycology. On off years, when there is no IDS, the North American Diatom Symposium (NADS) is held instead. The 19th NADS was held in the autumn of 2007 at the University of Michigan; attendance at this symposium is typically around 100 people.