The effect of Urumieh lake causeway in water quality and hydrological connection Seyed Kazem Alavi Panah Professor, Iran Email: salavipa@ut.ac.ir Kamal Khodaei Shahid Beheshti University Abstract Some water characteristics, such as turbidity, salinity water, depth, and temperature have a great importance in the study projects in water body. There are many researchers that have paid much attention to these water characteristics. Urumieh Lake Causeway has an important role that can be attributed to its effect in connecting west and east Azarbayejan provinces. In this study, we hypothesized that this causeway can effect on reducing hydrological connection between both sides, of lake. Therefore, we attempted to study the effect of the causeway on some water physico-chemical and biological properties. Due to the synoptic view, remotely sensed data may exhibits some spatial variability of water quality parameters. In this study, we used the digital number of Land sat satellite Thematic Mapper (TM) data of two different dates in order to investigate the water quality parameters of the lake and the effect of causeway on the mentioned parameters. In this study, following image processing techniques were used: creating false colour composites, contrast stretching, spectral profiles of TM thermal and TM reflective bands, selection of small representative area, from lake margin to the center for studing spectral behaviour of sediment and solute water. The obtained results have shown the capability of remotely sensed data in detecting spatial variability and distribution of water quality parameters. Based on the obtained results from spectral behavior, we may conclude that there are significant differences between the water quality parameters of two sides of causeway. The results obtained from variation of TM thermal DN values also show that differences. TM thermal and TM reflective bands are powerful in detecting water turbidity and salinity. The TM3 and TM6 have more important role in spectral reflectance of saline and turbid water in comparison to other TM bands.