Freshwater ecosystems around the world have been classified into lotic and lentic systems, that is systems comprising of flowing or standing water. There are varieties of plant and animal communities in these ecosystems and these have adapted to the physical conditions around them. Fishes, aquatic invertebrates, amphibians, crustaceans, diatoms, plankton and some aquatic plants form the important communities in these ecosystems. Fishes also form a very crucial part of the food chain in aquatic ecosystems, and occupy various levels in the trophic hierarchy.

Environmental pollution, mainly of water sources, has become of public interest (Niemi et al., 1990). Not only the developed countries have been affected by environmental problems, but also the developing nations suffer the impact of pollution (Listori and World-wide Bank, 1990), due to unplanned developmental activities associated with the exploration of virgin natural resources. Surface waters are vulnerable to pollution due to their accessibility for disposal of polluted runoff and wastewaters. Quality of the surface waters are altered by both the natural processes, such as precipitation inputs, erosion, weathering and  the anthropogenic influences such as agricultural activities, urban, industrial and increasing exploitation of water resources (Jarvie et al., 1998). Rivers play a major role in assimilation or carrying off the municipal and industrial wastewater and run-off from agricultural land. The surface run-off is a seasonal phenomenon, largely affected by climate in the basin. Seasonal variations in precipitation, surface run-off, interflow, groundwater flow and pumped in and outflows have a strong effect on river discharge and subsequently on the concentration of pollutants in river water (Vega et al., 1998). Since, rivers constitute the main inland water resources for domestic, industrial and irrigation purposes, it is imperative to prevent and control the rivers pollution and to have reliable information on quality of water for effective management. These impacts reduce both water quality (Sweeting, 1994) and biological diversity of aquatic ecosystems (Maddock, 1999). In view of the spatial and temporal variations in hydrochemistry of rivers, regular monitoring programs are required for reliable estimates of the water quality and conservation of riverine biodiversity. The integrated aquatic ecosystem management requires proper study for sound understanding and effective management of water systems and their internal relations and hence an attempt has been done in the present study to determine the water quality status and application of diatoms as a bio-indicator in the rivers of central Western Ghats.

The Western Ghats of India, is one of the global biodiversity hotspot, is a chain of mountains on the Western Coast with about 1600km long and about 100km wide stretch (between 8°N-21°N). The region has varied forest types from tropical evergreen to deciduous to high altitude sholas. It is also an important watershed for the peninsular India with as many as 37 west flowing rivers, three major east flowing rivers and innumerable tributaries. The current research focusing on five rivers in central Western Ghats monitors water quality along with diatoms, land use in the catchment and threats faced by these ecosystems.

Objectives: Main focus of the current research is to understand ecohydrology of west flowing rivers in the central Western Ghats. The work involved

1. Exploring the current water quality status of five rivers of Uttara Kannada district, Karnataka.
2. Assessment of the seasonality of diatoms and application of diatoms in biomonitoring in Western Ghats.
3. Understanding the impact of catchment land-use and land-cover on water quality and diatom community in streams.
4. Identification of the stretches with major water pollution and provide recommendation for mitigation and conservation of rivers of Uttara Kannada.