Rivers: Large natural streams of FRESH WATER formed by converging tributaries and which empty into a body of water (lake or ocean).Ross River virus: A species of ALPHAVIRUS associated with epidemic EXANTHEMA and polyarthritis in Australia.Fresh Water: Water containing no significant amounts of salts, such as water from RIVERS and LAKES.Water Movements: The flow of water in enviromental bodies of water such as rivers, oceans, water supplies, aquariums, etc. It includes currents, tides, and waves.Water Pollutants, Chemical: Chemical compounds which pollute the water of rivers, streams, lakes, the sea, reservoirs, or other bodies of water.Water Pollution: Contamination of bodies of water (such as LAKES; RIVERS; SEAS; and GROUNDWATER.)Environmental Monitoring: The monitoring of the level of toxins, chemical pollutants, microbial contaminants, or other harmful substances in the environment (soil, air, and water), workplace, or in the bodies of people and animals present in that environment.Fishes: A group of cold-blooded, aquatic vertebrates having gills, fins, a cartilaginous or bony endoskeleton, and elongated bodies covered with scales.Water Microbiology: The presence of bacteria, viruses, and fungi in water. This term is not restricted to pathogenic organisms.Seasons: Divisions of the year according to some regularly recurrent phenomena usually astronomical or climatic. (From McGraw-Hill Dictionary of Scientific and Technical Terms, 6th ed)Water Quality: A rating of a body of water based on measurable physical, chemical, and biological characteristics.BrazilGeologic Sediments: A mass of organic or inorganic solid fragmented material, or the solid fragment itself, that comes from the weathering of rock and is carried by, suspended in, or dropped by air, water, or ice. It refers also to a mass that is accumulated by any other natural agent and that forms in layers on the earth's surface, such as sand, gravel, silt, mud, fill, or loess. (McGraw-Hill Dictionary of Scientific and Technical Terms, 4th ed, p1689)Floods: Sudden onset water phenomena with different speed of occurrence. These include flash floods, seasonal river floods, and coastal floods, associated with CYCLONIC STORMS; TIDALWAVES; and storm surges.Population Density: Number of individuals in a population relative to space.Ecosystem: A functional system which includes the organisms of a natural community together with their environment. (McGraw Hill Dictionary of Scientific and Technical Terms, 4th ed)Water Pollution, Chemical: Adverse effect upon bodies of water (LAKES; RIVERS; seas; groundwater etc.) caused by CHEMICAL WATER POLLUTANTS.Catfishes: Common name of the order Siluriformes. This order contains many families and over 2,000 species, including venomous species. Heteropneustes and Plotosus genera have dangerous stings and are aggressive. Most species are passive stingers.Geography: The science dealing with the earth and its life, especially the description of land, sea, and air and the distribution of plant and animal life, including humanity and human industries with reference to the mutual relations of these elements. (From Webster, 3d ed)Cyprinidae: A family of freshwater fish comprising the minnows or CARPS.Biodiversity: The variety of all native living organisms and their various forms and interrelationships.Trematode Infections: Infections caused by infestation with worms of the class Trematoda.Otters: Fish-eating carnivores of the family MUSTELIDAE, found on both hemispheres.Population Dynamics: The pattern of any process, or the interrelationship of phenomena, which affects growth or change within a population.Onchocerciasis, Ocular: Filarial infection of the eyes transmitted from person to person by bites of Onchocerca volvulus-infected black flies. The microfilariae of Onchocerca are thus deposited beneath the skin. They migrate through various tissues including the eye. Those persons infected have impaired vision and up to 20% are blind. The incidence of eye lesions has been reported to be as high as 30% in Central America and parts of Africa.Fish Diseases: Diseases of freshwater, marine, hatchery or aquarium fish. This term includes diseases of both teleosts (true fish) and elasmobranchs (sharks, rays and skates).Water Supply: Means or process of supplying water (as for a community) usually including reservoirs, tunnels, and pipelines and often the watershed from which the water is ultimately drawn. (Webster, 3d ed)Sewage: Refuse liquid or waste matter carried off by sewers.Salmon: Fish of the genera ONCORHYNCHUS and Salmo in the family SALMONIDAE. They are anadromous game fish, frequenting the coastal waters of both the North Atlantic and Pacific. They are known for their gameness as a sport fish and for the quality of their flesh as a table fish. (Webster, 3d ed).Simuliidae: Several species of the genus Simulium (family Simuliidae) that act as intermediate hosts (vectors) for the parasitic disease ONCHOCERCIASIS.Dolphins: Mammals of the families Delphinidae (ocean dolphins), Iniidae, Lipotidae, Pontoporiidae, and Platanistidae (all river dolphins). Among the most well-known species are the BOTTLE-NOSED DOLPHIN and the KILLER WHALE (a dolphin). The common name dolphin is applied to small cetaceans having a beaklike snout and a slender, streamlined body, whereas PORPOISES are small cetaceans with a blunt snout and rather stocky body. (From Walker's Mammals of the World, 5th ed, pp978-9)Fisheries: Places for cultivation and harvesting of fish, particularly in sea waters. (from McGraw-Hill Dictionary of Scientific and Technical Terms, 4th ed)Alphavirus Infections: Virus diseases caused by members of the ALPHAVIRUS genus of the family TOGAVIRIDAE.Phylogeny: The relationships of groups of organisms as reflected by their genetic makeup.Conservation of Natural Resources: The protection, preservation, restoration, and rational use of all resources in the total environment.Animal Migration: Periodic movements of animals in response to seasonal changes or reproductive instinct. Hormonal changes are the trigger in at least some animals. Most migrations are made for reasons of climatic change, feeding, or breeding.Phytoplankton: Free-floating minute organisms that are photosynthetic. The term is non-taxonomic and refers to a lifestyle (energy utilization and motility), rather than a particular type of organism. Most, but not all, are unicellular algae. Important groups include DIATOMS; DINOFLAGELLATES; CYANOBACTERIA; CHLOROPHYTA; HAPTOPHYTA; CRYPTOMONADS; and silicoflagellates.Invertebrates: Animals that have no spinal column.